Welcome , you are among friends here !  super tough situation your in but all i can say is you need to put you and your son first, straight up !   I was in a very similar situation to you when i first met my parnter (now ex).  He was going through a nasty seperation that dragged on for years and years,, they owned property together and that dragged on even longer as neither one of them would do anythiing about ,,, i will say ,, i hope this man is efficient in his dealings and sorts out any assest division etc and doesnt let it drag,,,, if you feel he is already putting his head in the sand get out now !!!!   Also i can relate to being pregnant to these type of men ,, (this may be a touchy subject for some , but just trying to help)  i too also fell pregnant to this man,,i chose not to continue through with the pregancy and im so glad i didnt.  My son  from a previous relationship is about to turn 19 and we have a great relationship and if i had of continued through with the pregnacy, i would have been alone raising a young child to a man that cant get his shit together.     This man should not be parenting your son and you dont need to parent his brats.  His kids are the way they are becasue of both parents poor parenting, and this is not a job you need to take on.  you have only been with him for 18mths , my advice and most people on here are going to tell you the same thing...RUN

I think you should make an exit plan.  You sound scared and shaky but I think you know you need to leave.  As tough a decision as it must be, I'd not continue the pregnancy.  Take care of you and your son, those are the priorities.  Very best luck to you and im hoping for your best possible outcome.

...they won't be going away. In fact, things will likely get harder. As the girls get older, they are almost guaranteed to get more difficult (dear god, teenagers...). If you stay, the BM will almost assuredly be triggered by things in your relationship and lash out (especially if this is already acrimonious). And if you continued with the pregnancy, it will be monumentally more difficult. If it was me, I would probably terminate the pregnancy and leave the relationship. Focus on your son and yourself. That doesn't make you a terrible person. Also, from my own experience, that first relationship right out of a divorce is intense (maybe too intense) and is hard to see clearly. I'm glad you see these red flags now, and I know leaving will be difficult if you decide to go that route, but it can and will be so much better. you're strong enough to do it, and it sounds like it will definitely be better for both you and your son.  

My sometimes not so dear DH had a particularly nasty split with his ex wife. And she poisoned their daughter against him. Then I got pregnant with our own DD. At first I thought I found someone loving, attentive, dependable. He was funny to be around and said all the things I wanted to hear. I believed we were a team that could overcome anything. I believed it would shatter me to lose someone as wonderful as him.

Turns out with time his ex got no less crazier and he had the choice to be a doormat to see his daughter or develop a spine and never see her again. He chose doormat. After countless lies about money he'd diverted to fund his precious princess who only picks up the phone for money I've lost the respect I used to have for my husband. I've also found it especially hard to ever trust him again. Where once I thought I wouldn't be able to cope if he wasn't in the world, nowadays I'm just apathetic. 

Your own partner will always be the rope in the tug of war game. Torn between daddy divorce guilt to his precious princesses and trying his best to be disney daddy of the year and his relationship with you. You will always be put second because you're the dependable one vs the volatile first family. The double standards will grate on your son's relationship with him and eventually with you for bringing him into this not so blended family. My point is that this situation you're in won't change. Up to you if you want to bring another life into the mix but having babies don't fix problems. They bring forth more. If I thought SD and DH's ex couldn't get any crazier they certainly proved me wrong after my DD was born. 

I'm very pro-choice, but that's a big decision to make given that this is a wanted child. You can leave and keep the child - will it be stressful to deal with the child's father? Yes, but not impossible. He won't likely get any type of joint custody until the baby is at least 2 or so, as most states don't see it in the child's interest to be passed back and forth as an infant. You aren't saying he's an abusive father, so your child spending time with him won't be dangerous.

I don't think your choices are stay or terminate the pregnancy, I wouldn't think about it that way.

Babies rarely, if ever, make things better. There is some temporary bubble of love that happens upon arrival but that bubble bursts rather quickly. 

I also don't think that you should be worried about how your son will feel about you expanding your family and having another child. That is not his choice and parents should not allow their kids to have that much power. 

I don't know if I am prolife or prochoice anymore- I am just thankful that I have never had to be in the situation where I had to think about it. That being said, in my opinion abortion shouldn't be an "oops, I changed my mind and don't want this baby anymore". 

Live apart. Establish your own home and routine again. Nothing you said indicates he is a horrible father, just a lazy one. You can come up with a good parenting plan together to give that baby the best life possible with 2 parents that love him/her, maybe just not each other anymore. It takes work, but it sounds like you already have a good relationship with your son's father, so you know how to do it. 

When it comes to your stepkids, you are upset about how they appear and aren't allowed to discipline- that is most of the step parents in this world. I would do anything to be able to cut off the stupid mullet that my stepson has. I have to create a fuss over my other SS bathing almost everyday. If you want to stay and you don't have the power to change the kids- disengage. 

Let them stink, let them be dirty. Don't cook, don't clean, don't do anything. If they leave things around after they go back to their mother's house, dump it in their rooms or clean it up by putting it in the trash. It is passive aggressive but also a lifesaver technique. 

Take some time out alone. If you can. Reach inside yourself and listen to that inner voice. If you pray, pray and listen.

I am 53, with no bios, so my opinion would be keep the baby. But this is YOUR life and you need to do what is best for YOU and your SON. The fact is that you are not compatible with this man. You can twist yourself into a pretzel in several different ways to "make it work". It wont be impossible, but is it going to be miserable for you and your son? The skids will probably get worse over time. Their parents are failing them, the BM is super toxic and out for destruction, but at the core of it, this guy wont allow you in there, doesnt accept you as his partner, an equity partner. He is critiqing your parenting and your child. Hes not accepting your son.

Id bail and keep child, but again, you need to listen to what your heart is going to tell you. Talk it out here as much as you need to.

((( HUGS)))

Please do not continue to sacrifice yourself on the alther of your SO's crappy parenting and failure to be your equity life partner.

Do what you have to do to leave and take your own child(ren) with you.

Is it possible you've made your decision and feel guilty about that decision and looking for validation?   

Your body, your choice.