Just like for me, after my wife had cheated, I was clear that I couldn't be in a r/s with her if she stayed in contact with the guy. I couldn't heal that wound while she was still cutting away at it.
That is what is so hard for me on this board. I have a feeling that some people on this board see me as the other woman. I can't live with that. It is ironic that a former therapist said my SO was in a dead marriage and that if my SO did indeed leave his wife for me that I would get what most women in my situation dream of. I don't feel good about the fact that my SO is leaving his wife for me. The only thing that makes me feel good about that is the fact that he divorced her once before but then went back to her because he felt guilty. I have to remember that because I do feel that makes a difference.
Sorry for picking that example--I was comparing the resentment you are feeling to what I was feeling a year ago when I was going through the ending of my marriage.
You are judging yourself about being the "other woman" plenty all by yourself. I can only speak for myself, but I'm not. I'm mainly feeling compassion for the complicated mess you've ended up in.
It really seems like it is the financial/logistical problems of that circumstance without the normal emotional role it has, as he has moved out and (mostly) split financially, if not legally. And realistically, the degree of emotional enmeshment/garbage your SO has with his wife could easily exist in other guys who are already divorced. It is a different problem.
I'm not sure how much the prior divorce/remarriage makes anything better, but that is me. If you take comfort in it, good.