You know - in light of the fact that your other 3 kids are not his, and your D16 is acting out - I think you need to put a stop to this. Your kids deserve better than to be sucked through this drama with a man who is not their dad ( unless he raised them from a very young age and they thought of him as dad, but that's not your sitch, is it?). Think about what you are modeling for your D. Do you want her to think this kind of behavior is okay for HER to put up with from HER future boyfriends?
You need to put your attention on your kids right now. Every moment you spend wondering about H and OW is a moment you're not focusing on what's happening with your kids. Your D is possibly resentful that she's being pushed aside for a new baby, or that she has to carry more of the load at home, or that you're so consumed my H you're not focusing on her, or that you "pushed away" stepdad, or that you having a baby with H means she'll never ever have that fairy tale of her parents reuinting - who knows. But your exH seems to recognize that this sitch is not good for the kids - I'd trust him on this.
Let go of H. Spell out for him, just once, in writing, what it would take for him to come back into your life: 6 months of AA, no contact with OW, consistent appropriate behavior, etc. Don't set the bar too low. He may or may not be able to rise to the occasion, but trust me, you DON'T want him back unless he does the things a SINCERE person would do to win you back. Don't settle for less.
