I posted the above because I am worried about the future and am trying to learn everything I can about this so I can hopefully nip problems in the bud before they get out of control. I am in the unusual position of having thoroughly researched what I am getting myself into and not walking in with my nose in the clouds expecting life to work out with the SS when the BM is extremely high conflict. Here is the situation-

First off, let me mention that the child is a result of condom sabotage so you understand what kind of BM I am dealing with here. BM still lives with her parents, the woman is a child herself. She has never had a job, and has never had to do anything for herself. She is an only child and believes the world revolves around her. When I first started dating my BF 6 months after she dumped him, BM decided he would no longer be permitted to see the child at all, she cited me as the reason. Which is when he filed to establish paternal rights. Between locating her to serve her and getting a court date, this took 6 months during which she completely denied visitation. During that time she sent him several messages stating that if he asked to see his son again she would file for a restraining order, and a few more threatening him- telling him to sign over his rights to the child or else. In other words, completely insane. When they went to mandatory mediation, BM refused to mediate unless I was brought in because she wanted to meet me. She then decided that I was safe to be around the child, but insisted that the father was not, even though her original issue was me. She then began allowing visitation, but now was insisting it be supervised by me. A lot more craziness was involved (she denied paternity, made false domestic violence allegations, etc), and eventually the case went to trial.

Unfortunately, the judge had another hearing that ran over, and didn't want to stay late. So he refused to hear evidence outright, announced it was a new day and he didn't care who had done what, that they both produced half a child and they were both getting 50%, and he couldn't care less what evidence they had. The father lived in a different county, so he made up this roughly 50/50 schedule where the child would attend school in the mothers county (because the courthouse was located in the mothers county,) but the father gets 3 weekends a month (till Monday morning) and alternating holidays and the entire spring and summer breaks (save for 1 week). It came out to like 45% to the father, but he gets the bulk of the child's free time so he didn't complain.

Considering how insane this woman is, I forsee heavy duty pathogenic parenting on the horizon. We don't even have the final CO yet and she is already in contempt, but that's a separate issue. BM's father has already apologized for his daughters behavior to us- he has told us she has been coaching the child to call dad by his first name, and that he has had to ask his daughter to stop referring to the father as "the monster" and that he has repeatedly asked her to please stop telling the child that his father doesn't love him and wants him to die-- but says he can't control what his daughter is going to do. The child has also picked up this weird habit of constantly asking where I am at all times when alone with my BF. We suspect it is because she has told the child he is not safe unless she or I are present and that he is not allowed to be alone with his dad. My BF receives constant criticism from her via text and at the exchange. Sooner or later she is going to directly step on my toes, at which point I will stop being nice to her. (To placate her somewhat I have been sending her pictures of the kid when he's with us, checking in with her a few times a day to let her know her son hasn't fallen off a cliff yet, etc.) When I get fed up with her and stop trying to be civil (because I am really at my wits end with this nut job) she is going to start talking constant crap about both of us.

And I personally do not want to end up dealing with a SS that hates me because his mother has trained him to and a SS that refuses to see his father because his insane narcissistic mother has forced g-d knows what into his head. I foresee enough behavioral issues cropping up in a kid partially raised by someone that unstable to begin with. I know that if my BF had EOW, there probably wouldn't be much we could do, but with this arrangement we have a chance. (Although it wont be nearly as easy as if she only had EOW.) I don't know for sure how to proceed on this. This is one of those things where everyone tells you to "take the high road" but taking the high road clearly doesn't work, so I don't know what to do. Everyone tells you to never speak poorly of the mother in front of the child, but it would really be best if the child understood from a very young age that mom is a few cards short of a deck. Ideally, my BF and I stack the deck against her so her efforts backfire. But I do not know how to do this. That's what I was wondering has 50/50 custody and one parent trying to alienate the child from the other. I am foreseeing the issue before it occurs and am trying to take preventative/defensive measures. I need to know what to do.

I need to give you more on the dynamics to respond-

We were together before for 3 years. We were best friends for 5 years before that. We broke up over a bunch of extenuating circumstances and were both seeing other people for a while, (no commitments) but were still on good terms and were talking about getting back together. Nobody cheated, he was free to do what he wished as I was I, and we both knew what the other was doing. We were both counting on condoms being 99.9% effective plus supposedly she was on birth control. The now BM wanted a commitment and he wouldn't give her one. She secretly stopped taking the pill and slit the corners of all the condom wrappers with a razor blade because she knew he was going to leave her and go back to me if she wasn't pregnant- and it worked. She correctly assumed that he wasn't going to leave her with child. She didn't count on getting bored of him a few years later and the two of us then working it out.

Part of her insane behavior is because she knows the child is the last thing he wanted, so in her head that means he doesn't love the child and hopes it dies. She believes that he would just allow the child to wander off into traffic in the hopes it would solve the problem she caused and has told me as much. (Hence what she has been telling the child) Another part of her insane behavior is BM essentially forced herself pregnant to get rid of ME. I was the ex that her new boyfriend wanted more than he wanted her and it drove her insane with jealousy. She pretty much "made the ultimate sacrifice" to keep me out of her life and keep the boyfriend from going back to me. So the way she sees it is, she failed, I showed up and have more or less collected the boyfriend, and now I have taken her son along with him. The woman she sabotaged birth control to eliminate from her life will now be helping to raise her son.

In other words, BM is living her worst nightmare right now. She self manufactured this situation by being insecure and unstable to begin with, but me being the SM is literally her worst nightmare. She forced a child upon a man who was very clear he didn't want one, and the man has now stepped up and dragged her through the courts for partial custody when she honestly believed he would simply go away after they broke up. She's being nice to me because she is less worried about me right now than she is worried that the father might attempt to eliminate the child because he didn't want a child with her, and she believes if I am on her side, I won't allow him to hurt her son.

This dynamic, aside from resulting in an absolutely looney BM does give me an advantage as a stepmother. DH never wanted a child with anyone but me, and as far as he is concerned I should have been his son's mother. The only reason I wasn't is because BM insane and manipulated the situation to what she believed was her advantage. Without her horrific act, it would have been my son. Which means he has no respect for her as the child's mother. After she completely denied visitation for six months which left the child with noticeable trauma issues, (the three year old now has panic attacks when daddy leaves the room) he has no respect for her abilities as a parent either. He also understands that his having a child with another woman is not exactly an ideal situation for me, and he feels very badly about it.
This means the relationship is his first priority. There is no possibility of Disney dadding or catering to BM's wishes. He's been pretty clear I have equal say over how his son is raised and he may even grant me permission to override him if I can back my perspective up because he's the one who was dumb enough to be trapped by her in the first place. I am expected or required to do absolutely nothing for the child as he recognizes it's not mine, which means I only do what I want to. In other words I read bedtime stories and have pillow fights while he bathes, wipes, dresses, and feeds him. We went away for the weekend and I was expected to do nothing more than sit in the hot tub with a glass of wine laughing at him while he chased the toddler back and forth across the pool for three hours while completely exhausted, it was pretty funny.

The traditional stepmother enters the situation from an inherent position of weakness because the kids were there first and she is the "new" thing or the "outsider" that the husband now needs to integrate into his life. In my case I am the "normal" or the "constant" and the child is the new thing that needs to be integrated into both of our lives. Yes the child is three and not exactly an infant, but BM made it difficult for him to be involved from the beginning, even when they lived together. She agreed to give the child his last name so he wouldn't argue with her, but secretly wrote hers on the birth certificate. She stayed home and took care of the kid or delegated it to her parents, while he worked all the time. He had to take her to court to be allowed to be a parent to his son, so in that sense it's kind of a new thing.

The reason why I have been doing some of the dealing with her is because he's too angry with her to be diplomatic. The way he sees it this woman ruined his life for her own gain, and has now set out to ruin his sons too. The only thing this woman loves is herself, and the child is merely an extension of her own greatness and a trophy for her. He's also pretty angry about 10,000 in legal fees (while he's in college no less) to just be allowed to SEE his child. I can't say I disagree with him, however I figure stirring the pot when you're already dealing with a maniac is probably not a great plan. I don't think its good to allow him to antagonize her right now, at least not until the ink on the court order is dry and we have worked out a BM management strategy.

So with all that said, she is likely going to spend the next 15 years doing whatever she possibly can to turn the child against him and I. We are united front and have the child 50% of the time, so how do we counteract her poison?

It seems like if on this forum the poster is usually the bunny rabbit. Let the internet trolls do their worst.
I only spoke about DH's feelings on this woman's behavior and what it means for how he will handle the situation, I never spoke of my own. But sure, I'll lay it down to brass tacks.

If a woman is raped and concieves, and the pregnancy comes to term, I think most people would react with revulsion to the rapist receiving even partial custody of the child if he wanted it. They would all agree he should have to pay child support, but people will shudder at him having even supervised visitation, let alone 50% custody. Hey let's even assume that the rapist really wanted the child, and plans to be a great father. Let's argue the only reason he raped her is because he couldn't afford a surrogate and had some kind of ball cancer and this was his last and only chance to have a child or something like that. None of that matters does it? Something in your chest still recoils at the idea of bestowing him with the honor of "father." And the reason why people emotionally recoil is because he only achieved that status by violating someone else.

A woman who sabotages birth control violates someone in the worst way possible short of murder. A child being an accident is one thing, even a child born of rape is still an "accident" it probably wasn't the guys intention, plus the woman still has the option of an abortion. A man who uses birth control is not planning on a child. He recognizes that a child may occur accidentally, but the risk of child is extremely small, with 2 forms of birth control the chances of an accident are less than 1/1000, even with regular intercourse over the course of a year--meaning the chance is small enough to be negligible so he doesn't really worry about the risk of sex. Now when someone sets out to become pregnant, the chance of pregnancy suddenly skyrockets to 75% per individual incident of intercourse. If the man knew that the risk of getting the woman pregnant over the course of a year is greater than 100% (as it is when someone fertile sabotages birth control) there is absolutely no possibility he would have slept with her voluntarily.

This is a much worse violation than simple rape. In rape the only violation is the intercourse. In this situation? The man would not voluntarily have sex with her if he knew about her deception, so the intercourse while "voluntary" is a violation of his body just as it would be a violation of a woman's body when she is raped. In addition, she has subjugated his free will and taken his reproductive freedom away from him, violating him at the deepest level by forcing a child upon him, which he then has no choice in whether or not to keep. This child is no accident of fate, it is a burden she forced upon him by choice. She has dictated the course of the rest of his life by her act, and he is absolutely powerless to do anything about it. A rapist violates only the body, a birth control sabotager violates the soul as well.

So to be honest, yes, I do believe you need to do a little more to earn the title of "mother" than spread your legs while intentionally subjugating someone else's free will. If this belief makes me out as the bunny rabbit and renders me as a sacrifice to the legions of internet trolls, so be it. I do understand that some women do this, some women even feel that they have the right to do this, but it is a truly awful thing. People may not agree with me, but its difficult to respect her as a "mother" for the same reason that the same people would believe a man needs to do more than rape someone to earn the title of "father."
And even if we are going to sweep all that under the rug and say its the man's fault because he decided to have sex and the rest of the situation doesn't matter, we also have a mother who is damaging her children. A mother who after 3 years completely cuts the father out of the child's life and starts telling the child he has no father? And when the father refuses to go away she tells the child his father doesn't love him and wants to kill him? Do you know what kind of damage this does to a child? This kid is barely old enough to talk and she's already taught him insecurity and self hatred. She has somehow created a 3 year old who has panic attacks. (Not tantrums, panic attacks) I feel the same way about the drug addicted BM's who want nothing to do with their children. If you can't act like a parent I do not believe that you should be respected as one. The kids may choose the bio parent first but that's a mistake on their parts when the bio-parent is useless and I won't support it. They are kids and only know what they are taught. Clearly some children need help learning to choose better.
You tell me that logic doesn't work in step-parenting and maybe it doesn't, but it should. Just because step-parenting apparently totally sucks doesn't mean all stepparents should just lie down and let the BM and BF dictate how this is going to go just because they happen to be related to the child. I mean, these are our lives too. We have a right to control our own homes, and we have the right to control how children who live under our roofs are going to be raised. And I understand the whole disengagement thing, and not doing too much for children who will probably never love us unconditionally the way they do their parents because they aren't blood related, but you know what? I don't think that means we should all automatically give up. Children only know what you teach them. Stepparents do not have a set "role." Most of them try not to step on the bio parents toes. I am going to make up my own role if I have to and if someone's toes need to be stepped on, I am willing to step on them. Besides, if you're going to call us "step"parents doesn't that imply it's our job to step on the parents when necessary?

But realistically, I am not really all that spiteful. For the most part I don't waste my time with it. I'm not confrontational and for the most part believe in live and let live no matter what someone does to you. I feel bad that the woman is so crazy and feel bad that her own parents did such a poor job of raising her that she behaves this way. I wish her the best and certainly hope she sees the error of her ways some day, but I am not going to bow down to her and will do whatever I need to do to defend myself and my DH. And to defend my DH I need to defend the child against her poison too, whether its my child or not. And if the child wishes to bow to her because she gave birth to him that's certainly his right, but I will not support it and nether will my DH. Whether or not the child ever finds out we don't support it,we don't know yet, we still need to figure out what's best for the kid which is why I keep posting because I am trying to figure out how its best for us to proceed.

In its simplest terms- My DH is 100% supportive of me, the child is very sweet, and the only problem with the situation right now is that we already recognize that BM is nuts. I need to figure out what I need to do or what my DH needs to do when the other parent is actively trying to turn the child against him or us. We need to work out a battle plan, and we need to do it now BEFORE her behavior begins to affect the child and become a problem for us. I understand my role is to support him and that's all I am doing. He wants to know what he can do as the father to control what goes on in his own house when he has only has his son half the time and the other half of the time the child is in an extremely toxic environment that he cannot control. I am trying to help him figure it out.

Well, no I don't disagree with you. You are correct in that it is a violation on multiple levels, I just didn't state it that specifically in my post.