I'll give you my two cents and that is all it may be worth:
1) Guys generally (including me) really do react to pressure on the things you are concern with very well. I'm not surprised he improved when you backed off. I would guess he will again.
2) I'm struggling with the same thought process. Maybe my W and your H need to miss us a little. I don't know that answer. There may not actually be an answer. The decision I'm coming to is that I need to do what is going to make me feel better. I don't know what that is right now absent her forcing my hand by dating. But, I'm leaning towards separation. I'm going to talk to my lawyer and a DB coach next week. I'm happy to share their collective wisdom with you if you'd like.
After all that, I'm glad that your son is feeling better.
