Grace, I think you handled yourself so well. Much better than I know I could have done where you are. Definitely with grace and dignity. Yours is like the lab rat for the DB method. You push the button, he responds on cue.
But, I don't see so many airy fairies here. Your guy is a talker. He shares his feelings often and with everyone it seems. But where is the action? I don't see anything concrete in what he said to you. And it doesn't seem that different from what has been going on. But then you know your own story better than any of us ever could.
Is him saying things aren't going well with the OW any different than him likely telling her how awful the marriage was, how he couldn't take it? I see this as SOP for these guys. I've read so many threads here and elsewhere where they say that and it doesn't change.
I think you are seeing fear. Fear that his safety net will be gone. Indecision and confusion. It looks promising, but it is all about him. Again, mine doesn't talk, but I have seen that same fear. The crazy cycling, the inability to let go. Don't know about yours, but with mine that same indecision took him forever to leave and would take him forever to come back if it were in the cards. That same attachment that makes it hard to end things with you is going to make it hard to end things with her.
Don't discount your daughter's feelings here. Mine told me straight up a few weeks ago that she would lose all respect for me if I let him back. If it ever comes to that, make sure your daughter is at least open to you giving him a chance. I think the only thing worse than losing my H would be losing one of my children.
He's doing what he's doing because he is seeing your strength and resolve. My guess is that if he saw you relax and step back, he'd feel safe again and go back to runaway teen.
He's given you a road map here. Will you hear from him in 2 days? Will he accurately communicate what transpired? Will he lay down the next item on the agenda to getting out of where he is. Have a little hope, but do it with your eyes wide open and make him show you ACTIONS.