I think that they frequently rewrite history. If they could see their reality for what it really is, I highly doubt they would like it.
My STBXAH does the same thing. However, he cheated. He now claims that it is because I fell out of love with him, because I became too involved with the kids, because I am crazy, or because I was a mean, abusive wife. His truth depends on who is listening. I have had several friends all tell me different reasons why he claims he left me. (Even though I kicked him out...but he can tell it however he would like.) His reality is constantly in flux. It needs to comfort him. His reality makes him feel as though he is justified to drink, justified to do horrible things to me and our children.
I'm sorry that you are having to go through this, I know how freaking frustrating it is!