I agree with WDID, I doubt he understands whats going on. You should try to do somethings for yourself. If you read the books, try to do some of the 180's, if you normally react one way, try to figure out what the exact opposite reaction would be, Im not saying that you should stop yelling about the affair and be nonchalant instead, but maybe set up some boundaries, maybe ask for transparency with his cell phone bills? If he continues to contact this woman in a non-professional setting you aren't willing to try, or maybe he can try to find a new job. How do you react when he says its over? And when he says he wants to come home.

It sounds like he has a terrible self-esteem, if hes seeing this woman who he knows is attached to someone else?

I guess I gave the wrong finger to the wrong man...