If I were you at this point, I would completely stop validating, and the easiest way to do that is to simply stop talking to him. Go dark. Keep your responses short and limited to a few key phrases. Yes, no, okay, I need to think about it, I’d like to talk about that in person, I don’t think that is in D4’s best interest, I’m not going to discuss that with you anymore. That sort of thing. Physically, emotionally, mentally distance yourself as much as possible. Don’t worry about losing him. He is already gone. The goal now is to nurture and protect yourself. It’s all about you now. You could try setting a personal boundary that anything that happened in the past has no bearing on your coparenting relationship going forward. Don’t use coparenting as an entree into a relationship. Don’t acknowledge comments from him like “you always” or “you never” or “this is why I left”. Just decline to engage. Literally put the phone down or walk away if he goes there.
I can only speak to my situation, but there was a point that I realised XH’s view of me and our situation was totally skewed and objectively incorrect, and it would remain that way as long as he was actively in an affair. There is his truth and her truth, definitely, but there are also facts. He is welcome to his truth, and I was happy to acknowledge that his feelings about his truth were valid, but I would not validate anything that was not fact. That included any accusations about my character or my motivations. Ignoring these things is the most effective and protective response. Validating might have made him feel better, but it made me feel like dogsh1t. It became a vicious cycle of accusation and validation, and the only way to get off the awful merry-go-round was for one of us to stop participating. I realised XH was never going to stop blaming me and I no longer wanted to absorb those negative feelings. It was wrenching, but I had to cut contact.
I know the advice here is to always validate, but in my case, validating XH’s feelings actually fed into his victimhood narrative and fuelled his justification for leaving me. It made him more convinced that he was doing the right thing because I was admitting to all his accusations. He didn’t form his ‘controlling, manipulative, under the thumb’ narrative until AFTER I wrote him a heartfelt letter owning my part. Before that, it was all about how weak, boring and not-good-enough I was. Validating his ‘truth’ made ME believe that I was the horrible person he told me I was which I knew wasn’t objectively true. There is a lot of emphasis from pro-recon people on owning your part, but that doesn’t mean you have to believe everything he tells you about yourself. None of us are perfect, but you HAVE to back yourself. Trust yourself and your innate goodness. Know yourself and your motivations. You made mistakes, but you were committed, always. You gave your all to your marriage and your family. He didn’t because he left. That is a FACT.
It’s okay to put yourself first. It’s okay to admit you are a victim. You were abandoned and deceived and betrayed! You signed a contract in good faith and he broke it. You were emotionally mugged. If you were physically mugged, people wouldn’t tell you to own your part, would they? Anger and grief and disgust is a healthy and normal response to being victimised. Sit with those feelings as long as you need, but act on your principles rather than emotions. It’s okay to acknowledge that the person you loved more than anything didn’t love you the same way. It hurts. It really hurts. It’s okay to be angry with your H, while still loving him, and at the same time admit that you deserve to be treated better. My XH was my first love, and I doubt I’ll ever be able to rid myself completely of my feelings, but he did me very wrong and I won’t ever take him back. Use your strong emotions as fuel to close the door. Remind yourself you deserve better than table scraps of consideration. What you’re holding onto isn’t love, it isn’t reciprocated, it isn’t healthy. It’s hurting you.
Think about what you would tell your daughter if she was in your position and treat yourself with the same respect and care.
This is all just my opinion and I hope I haven’t overstepped with anything I’ve said. I’m really rooting for you!