Agree. The husband sounds like the male version of the walk away wife.
No he does not. A walk away wife does not have someone in the wings. She leaves, and is ALONE.
The op's husband is a cheater. He is living in unicorns poop skittles and vomit ice cream sodas land.
OP, I'm sorry that your husband has done this. IT IS NOT YOUR FAULT. If he was so unhappy, he should have been honest with you about his feelings BEFORE hooking up with another woman. The presence of another woman is a complete game changer.
My story is much like yours. My H "broke up with" the OW within 2 weeks of informing me he had not loved me in 5 years, and that there was no one else in the picture, he just wanted a D. Like your husband, he had been very loving up until then, although we had occasional normal disagreements. When my H broke up with OW, he came back to our family (me and 4 children at the time, 7 - 14 yrs old), and I took him back, I was so shell shocked, broken, and (throw up now) relieved he had "come back to his senses."
He now says he can't believe what he did, and the untrue hurtful things he said to me to justify it, and that marrying OW would have become a nightmare for him. (He got out of his nightmare, but my nightmare continued for quite a while after that.)
However, the damage was done (to our marriage, to me, to my trust.) He has spent the last 8 years trying to rebuild my trust, and I have spent the last 8 years trying to trust that what I see (him do) and what I hear (him say) are true. It is hard to forget the things that are said when they rewrite the marital history in an attempt to justify their affair.
What I should have done, is file for D immediately. Who knows, by now I might be happily single, happily remarried, IDK. At least I wouldn't be dealing with the reminders of the destruction caused by his affair and his hurtful words.
He apologized this morning because he realizes another permanent damage he caused, and he told me "One can't un-ring the bell" today. He says he wishes he could go back and re-live that period and do differently. But he can't. The damage was done, and I am now a different person as a result.
Elegirl is right. If you file for D, you don't have to follow through, but at least get it started. Take care of yourself first, and if you want him later, and he wakes up from his fantasy, you can take him back.