This sort of sitch happened to a girlfriend of mine over 30 years ago. She was head over heels in love with her H. They had one girl ~4 and she was pregnant with the second girl. She found out he was having an A, and she divorced him immediately. He married the OW, then divorced her several years later. He has since been married twice more and is currently married. He has maintained a R with the daughters over the years (they are now in their 30s). The younger girl was born after the D and once when she was in grade school, it dawned on her that her parents used to be married, and she said incredulously to her mom, "You mean you were married to my Dad?"
All this is apropos of nothing, I guess, except to say that my friend and I were talking about this at lunch the other day and she said her ex seems to like to be married and she guesses he just stopped loving her. This seems impossible to me. How do you just "stop loving" someone? Even if you meet someone else, you love them both and feel torn and choose one for good or bad reasons...
So far this has not been very helpful to you...
My guess is that he feels that he has gotten himself into a huge mess and sees no way out except to go forward. Like a guy who goes down a long tunnel and gets stuck and feels the only way to escape is to keep pushing forward. For some reason, the idea of backing out doesn't occur to him, or feels like some kind of defeat, when actually it's the most sensible way (since he knows the path) and the simplest.
I suppose it's possible that he's head over heels for the OW, but frankly, that doesn't seem likely either. It seems to me that as he sits in this giant boiling stewpot, he is looking for a way out-- not a way out of your M, but a way out from under the pile of sh!t he has brought down upon himself. If you do want him back, can you make the way back to you the easiest, least messy, most face-saving path? I expect that if he starts making noises about saving the M, the OW will start to pitch a fit and then SHE will become very unattractive. This is all just speculation. I haven't read up on your sitch, just wanted to throw in these comments for what they're worth.
You're in a really tough spot. I know that for my friend to give birth AFTER her divorce (she has a very supportive family and had moved back in temporarily with her parents-- she has six brothers and sisters who, with their children, are still a huge part of her life) was excruciating. To be honest, she's never quite "gotten over" that D.
