May can I tell you a little story about my exH. My exH went into a downward spiral after I left and as I built my self up and reclaimed my life, started dating, and then fell in love, my ex went into a deeper depresssion. Then one day decided he didn't want to be like that any more. Worked on himself a little. Started to date. Met a great girl. She was an absolute angel to D17. She came to every sporting event, every concert, every big moment. No hesitation. She made sure exH was there, was sober, was happy and attentive to his D. We loved her. She made my ex a better man. A better man than I ever could. And I did beat myself up about that for a while. I had so convinced myself that he was the toxic one I hadn't taken the time to realize we simply were toxic for each other. As their relationship progressed I accepted more and more that he and I simply weren't meant for each other. We weren't meant to be together forever. He was put in my life to give me my beautiful baby, who is no longer a baby. And that was his purpose. She is all the wonderful things about him. And she does carry a few of the not so wonderful things about him. Stinky feet, a need to sleep 10 hours or be a monster to deal with, etc. He got to be there for all her baby firsts. And some of her formative years. But at 9 her and I were on our own and she said she wished I had done it sooner. Because him and I together was terrible for her. In the years since ExH blew up that amazing relationship that made him a better man. He has a new trashy gf who has 4 kids from 4 baby daddies. She was married when they started sleeping together. ExH is drinking heavily again, and not caring for his mental health. And no matter what happened in this house D17 was helped by her parents splitting up.
All kids fair better in 2 households than then do in 1 toxic one. If your H won't put in the work your home will become so toxic it won't just be confined to the two of you any more. Toxicity like that seeps out, oozing all over everything. You can't control it either. It will effect your kids. And you have no idea in what way until it's too late.
You know how I feel about standing. If you can't, won't, or other wise are unable to be the one to pull the plug so be it. You stay. You figure this out. You do what you need to do. I am 100% on board with once you're done you're done, but you're not giving up with out a fight. I am that exact same person. If you aren't in a place to throw in the towel so be it. But don't stick this out for the kids. And sorry but a little 2x4 here don't say it's for the kids when it's not. Since this newest little revelation of H being a waste of oxygen you bring up the girls a lot but it's nearly always about how you think they are going to feel, and all of that is based on how you're feeling. Not the reality of how they will deal with things, because the truth is you don't know. Some kids take all of this stuff very personally, but most kids won't give a d@mn that they have a separated mommy and daddy once they start getting 2 christmases and birthdays. The wonderful thing about children is they are incredibly self involved by design. And also resilient. If you love them and support them to the best of your ability none of this has to affect them deeply or in the long term. If you always choose to put your daughters' feeling above your own regardless of the hate fire you have for H or AP or who ever may come in the future, you will always have well adjusted, happy girls. You're an amazing mother. And he's a great dad. The only thing imposing on them not having a rough go of it isn't you two separating and ending the marriage, it's you two in a constant power struggle for the rest of their lives. You don't have to be the bigger person now or ever. But as I've told wooba, I will tell you. Meet him where he's at. You can't expect rational behavior or logical, mindful choices from your H. The sooner you can start making the best decisions for you and the girls devoid of emotion the better. Because for the rest of the girls life you will have to be the bigger person. The more detached person. The water off a duck's back person. Because H isn't capable. You have to choose your battles. You have to choose your words. You have to make the hard decisions and swallow your ego more often than you should. But it's what we do as mothers.
Stay if you need more time to figure this out. Leave if you can't take this any more. But please don't do either based almost entirely on what you think the girls want or need. They need two parents who love them. That doesn't mean they need you together.