I think you dodged a bullet. You left when she became abusive, emotional abuse is just as bad as physical. 
 

You didn't do anything wrong you stuck to your guns. Lots of step parents/future step parents come here to find the strength to do what you did. 
 

You might be sad right now but if you hadn't followed your gut instinct would you be happier? I don't think so because she is going to continue that enmeshed relationship with her ex ya know "for the kids". 
 

Maybe you should find a therapist to help sort your feelings and rebuild. Take your experiences as lessons learned and keep listening to red flags in relationships. 

You did nothing wrong.  You played the part she wanted but when you wanted to move beyond that and actually be in a serious relationship it was time for her to kick you out.  She is enmeshed with her ex and is going to stay that way even though he makes her unhappy - your basic obsessive relationship.  Having a boyfriend is fun and exciting and lets her play jealousy games with the ex.  No new guy is ever going to "close the deal" with her.  Even her mother is participating in the crazy.  You are well out of it.  Be glad that you are out and find a nice woman to have a good relationship with.  You did nothing wrong here.

She is abusive. She also has an emeshment (and possibly emotional affair going on) with her ex and unhealthy patterns repeating themselves. When the relationship was new, the mother and her talked badly about her ex. Now they are talking badly about you. Give it time and they will both be talking badly about her new squeeze. Remove yourself from this toxic mess. You deserve much better than this. She is abusive and is not relationship material. It also sounds like she is also codependent as she always need someone around to take her problems out on and do her babysitting for her. When you refused to be that person she replaced you. What she really needs is to be single for awhile and work on herself and find out why she feels the need to be abusive and also codependent. Find someone who will treat you with respect. She did not respect you nor did her kids nor mother. 

And remain without this person in your life.

In therapy you can discuss why you need to be treated like dirt and used. Perhaps research codependency.

I dont mean to be trite. But my DH has co dependency issues and stayed with his now ex for more than 15 YEARS. And she treated him badly and was verbally and physically abusive.

You can remind yourself it was a good decision to leave just by how she reacted to you when you tried talking to her. The essence of a relationship, no matter what's involved, is being able to hear the other person out, come up with a compromise, and change behavior to make the relationship better. The fact that she shut you down when you tried bringing up your thoughts means she is the sole decision-maker in the relationship. That your opinions, thoughts, feelings don't matter. It is extremely difficult going into a step situation as it is. The only way it can be successful is if your perspective matters, your voice is heard and the things you want are factored in. She is very selfish and doesn't care about how you feel. If you get back with her it will be the same thing all over again. You did a really hard thing and you should be proud of yourself!

It's easy to think you wasted a lot of time, but you actually didn't. You grew as a person by a lot being in this dynamic. You also have a solid sense of what qualities are deal-breakers for your future relationships. 

I'm not sure how you know about what's going on in her life. If you're in touch with her or connected through social media, I would suggest cutting off all communication and blocking her. It's MUCH harder to move on when they're still in your face. Just feel sorry for the new guy and don't look back. You deserve so much more.

I'm about your age... if the way you describe yourself is true, you can do much, much better than that mess. Single, child-free, good-looking guys in their early 40s who are in great shape and have good jobs should have no problem finding a child-free woman to go have a really cool life with... the kind of life someone with kids can't have. But you have to believe that, believe that you're a catch. Sounds like this woman had a lot of unfinished business. Get a little therapy going and find out why you would hang around that shady situation. 

You didn't do anything wrong. You became involved with someone is not ready for a relationship and probably never will be. Quit worrying about her next relationship - quit following her on social media. It is time to move on.

I'm going to say this as gently as I can, and if I am wrong, please don't take it as an attack on you. If there is any possibility you are a member who has posted about this situation before under another name, please contact a therapist and get some "real life" help. You deserve to be happy, and your ex SO was not the one who was going to give you a happy life. You didn't do anything wrong and you need to understand that. It was your SO - not you. You need to let it go, learn from the relationship, and move on.

You didn't do anything wrong Move on. She didn't deserve you. She was abusive towards you and not emotionally available. She had no business being in a relationship and still doesn't. Let her be her current guys problem.

How did she move on so quickly?!! She was already cheating on you with her ex.  You say she and her mother claimed he was involved in drugs, I'm curious if she was as well and her mother is an enabler.

look at it this way, you managed to get out of this situation largely unscathed.  She has no claim over your money or your house, all things you could have lost out on had you married her.

I think she is the narcissist here (maybe not her ex) and the rest of it is standard stepparent treatment. Do everything for her and the kids and get nothing in return. Most of the time it’s a one way street because you’re never an equal priority to them. You always come last to the kids and they always have too much power in the home. Because your not “the parent” you are expected to shut up. But then when it’s convenient to them you babysit and do everything else for no thanks, because they just expect it. Good move leaving. Don’t look back. It’s something I wish I did at 12 months when the red flags started popping up. Now I have to stay and try to make it work, but my advice to friends is always the same. Think twice as hard before dating a single parent. Double standards and expectations everywhere you look. 

You cannot save or fix for the kids.  Enjoy the positives you had from them. She needs serious counseling and work an is in no way ready for a relationship.  If you value your health and sanity, cut all ties with her and never see her again.  Eventually, a woman who is ready for a real relationship will come along.

You did nothing wrong in regards to her.  However, one piece of honest advice I can offer..... Stop being so much a people pleaser.  I did this and it was my 50% for my first marriage failing.  You can indeed do too much and you cannot fix nor rescure someone.  Look instead for a true partner who will work alongside you in the relationship. 

OP you wrote:

 I was told by my her and her mother that he was a loser and during their marriage they fought a lot and she would call her parents to vent for advice. I was also told he never had what it took to be a full time dad and was very selfish.

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When I read this ^^^ I knew it was over for you.

. Run, do not look back. Right there is a what A PROBLEM looks like.  Girlfriend and Granny tag teaming is trouble.

**I will leave my own personal experience out of this--but please know, this is NOT good.**

Do not over look all of these flags.

This sounds exaclty like BM. She was verbally and emotionally abusive towards my DH. He told me at first things started out great. She convinced him to move to another state for her and he did. They married and had a child. As soon as the baby was born together things started to change. She became emotionally and verbally abusive towards him. She was always telling him his career was never good enough, he never made enough money, wasn't there enough for her (brat) kids from her previous relationship, and would even suggest to him how to dress, what to wear, etc and compare him to other men. On top of that she was seeing baby daddy number 1 on the side (he found out later after they divorced). She also had issues with rage and anger and would frequently blow up at him over nothing. Anytime he mentioned anything to do with her skids (who act terribly) she would rage and kick him out of the house. Finally, after breaking up and getting back together about a dozen times, he got the courage to leave and not go back. He filed for divorce and she was livid.  She bad mouthed him to her family and turned everyone agianst him by smearing his name (she did the same thing with baby daddy number one). 6 weeks after he left she met a guy online (a musician and you should see this guy, what a total dog compared to my DH who is very handsome) and she remarried right after their divorce was final. What a joke and this all happened while she was still trying to get my DH back and she never mentioned it to him. This devastated my DH as I believe he was used by her and also used to the abuse and had trauma bonding. My DH is good looking, stays in shape, dresses nice, works hard, and never understood what he did wrong. My DH stayed single for nearly four years then finally decided to get out and date again. Still to this day he has issues with anxiety and trust because of her. Luckily loving friends, family and a wonderful therapist got him through the worst of it. This can happen to men too and quite often these birth moms are ruthless. What ever happened to her homely musician husband? They are now divorced and she is now with another homely weird guy. I've seen photos of these men she has been with on social media since my DH left her and let me tell you they can't hold a candle to my DH, looks, career or otherwise. She had a true gem and lost him. Her loss. Now she has 3 kids with 2 different men and is on her fourth "serious" relationship in less then 7 years. Her cycle of abuse continues. The only issue is he is still connected to her because of their daughter who is lovely but BM is ruining her with her bad parenting and trying her best to turn her against him. She tried to get it to where he could not see her and he spent thousands fighting her on it and won. Good thing he has a good job and can afford great lawyers who won't back down to her manipulations. They are not scared of her and won't bow down to crazy. He won't be manipulated by her like baby daddy number 1 is. My DH is now trying to go for full custody of his daughter which I hope he gets. The funny thing is BM acts like she is a great hard working single mom who has it together yet needs a savior when the reality is all she ever does is take take take from people and uses and abuses those whom she is with. She is also in a lot of debt from her shopping compulsions and who knows what else. She is also lazy and on her phone constantly. She was always trying to get money out of my DH but has since backed down because of his lawyers. He is making sure his child support goes to his daughter, not her.  He is cordial to her because of their daughter but he will not be manipulated and used by her any longer like baby daddy 1 was and still is. She was also with 3 different men in a 5 year span who were around her kids and got to know them and now she is with a fourth man. I truly feel sorry for her kids because she is not a good mother. She lacks self refleciton and awareness that she is an abusive person. She needs help but I doubt she will ever seek it out. Abusers are truly terrible people and I do believe in karma.

What you did wrong was choose an entitled, manipulative, prior relationship breeding user and then tolerated her crap over and over and over again rather than telling her to FO the first time she played her games.

Grow some balls man and have some confidence.  You are a caring man but you have zero confidence.  People like your good riddance she is gone X should  not get second chances with decent men much less 7 years of chances.

Quit being such a sniveling cry baby and recognize that you are in a far better place with this toxic breeder, her spawn, her mother and her X fading into your past.  Why do you care that she has moved on?  It is far better to celebrate that she, her crotch droppings, her XH and her parents are out of your life.  

You did not invest 7 years on her and her spawn. You wasted 7 years of your life on them.  For something to be an investment it has to have a return.  Once it proves that it is a shitty investment it is time to cut your loses.  That point was years ago.   Hopefully you have learned something and will never again tolerate this kind of manipulative, characterless, manipulative entitlement breeder in your life any longer than up until the first time they pull the  kind of crap this toxic woman put your through for 7 years..

Just my thoughts of course.

Good luck

And enjoy your new life adventure with this POS and her shallow and polluted gene pool in your past..

Anyone who blows up at you for stating thoughts and opinions is not someone you want to be in a relationship.  Anyone who silences you or routinely breaks up and tells you to leave when they are upset is an a-hole. Let her stay in her drama and poor attitude. No man will eant to be with a woman like this. Also, she sounds enmeshed with her her ex and her mom. The new guy wont stick around. Also, her mocking you and saying Oh thanks for doing me the "big favor" of watching her kids so she could run errands, diminishing what you volunteered to do when you did not have to is all kinds of wrong. Idk why some of these bioparents think that anything steps do should be poo poo'ed. The fact is you didn't have to help her at all and she crapped on you. Ridiculous. Their rationale is completely stupid. She did you a total favor and sounds completely immature. Also, her saying you aren't fit to be a full time dad is ridiculous.  If you had your own kids they'd not say that; and also her kids have their own full time dad. Once again, it's a way of diminishing you. I'm angry for you and I'm so happy you got out  She is not good relationship material. Anyone who silences you and demeans you, diminishes what you say is not good partner mateirla.and thatvdoesnt get into all her issues with her kids, ex, their schedule, codependency,  her covering up hanging out with her ex and her nosy/gossiping mom. I'd never speak to her again. She was very rude and unkind to you. 

She did you a favour showing you her true colours. Please don't give her a second thought. You did nothing wrong and she should have never expected you to "babysit" her kids. The fact she said the same about the dad as she did about you tells me she is the problem and she manipulates and bullies her partners. That is an abusive relationship and I feel sorry for the artist. Fast forward a few years and I'm sure it will end the same for him. Move on and find yourself a genuinely nice woman.