Are you saying he got served with D papers? Sorry, I don't know your full story. Are you seperated? You say he is doing everything as states he wants the marriage. What do you want?
As far as the AP. Yes, it's his fault she is in your marriage in the first place, but if he has told her he wants his marriage and not her, and is NC you can no longer hold that against him. Is he willing to file a RO to get her out of his marriage now? I know that a lot of these OW fall in love (thanks to our spouses), when all the wayward really wanted was a secret fuckbuddy and ego stroker. Sorry about all the questions, I am just trying to understand what is going on in your sitch.