Ambivalent, I'm going to be very honest w/you...stop trying to rationalize w/him. His perception of his life is his own, just as your perception of your life in the marriage is yours. You know what is real and what isn't. Right now, it's Memorex time w/him and no matter what you say or do, it's not going to change his mind. Own your 50% of the marriage and let it go. Don't take on his 50%. Right now, he's looking to blame you for the sun coming up. You know what you did or didn't do in the marriage, accept your faults and move on. You are not going to convince him otherwise.
It's time to start focusing on you and what you need to do to survive. You can't rely on him because in his mind, the marriage is dead, over, kaput. In his mind, he's already moved on and you, the family and the marriage are an anchor weighing him down. He wants to cut the cord completely and the only way that he sees to do that is by divorcing you and leaving everything behind and starting fresh.
Again, the more you argue w/him, the more determined he's going to be that he's right and he did the right thing in moving out and getting on w/his life. His focus is on his freedom and being single and enjoying life without the responsibilities of a wife, family, home and bills. He doesn't realize at this time, that responsibility and bills will follow him wherever he goes and until he faces his demons, accepts that whatever happened long ago wasn't his fault, and accepts himself as he is today...he'll continue to make the same mistakes over and over again. You didn't break him, therefore you can't fix him. It's all on him to do this.
My advice, only deal w/him on expenses and legal issues. No more talks about the relationship. The more you talk about the relationship, the nastier he is going to get and believe me, you will see the exact opposite person come out and it's not pretty. They can get really nasty and say some extremely hurtful things that will bring your PMA right down into the dark hole.
Keep the focus on you. You know what your relationship was like and you know what you did or didn't do the relationship. There's not need to defend yourself now because you've had these discussions before...let it go. I know it's hurtful and you want to point things out to him...but it's not going to do any good but fuel your fire and make you angry and anxious. Take that anger and use it wisely in exercise and dance. Get it out of your system in other ways.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.