Grace, I do think you are thinking about it too much. You really don't have a decision to make right now. He is a talker and is sharing emotion, but when has that not been the case? I think you have to discount all the words and only look at the actions.
1. Seeing the therapist (great); 2. Telling you about the visit with the therapist (great); 3. Still hasn't left the OW (not great).
You do such a great job when you turn your attention to yourself and you are showing him the marvelous picnic you are having. Who wouldn't want to be at that picnic? What else do you need to do to hold the carrot out for him? Getting yourself wrapped up in what-ifs that haven't materialized and feeling the need to keep pressure and worrying about pressure--too much H focus. Focus on Grace and the picnic.
Get the post-nup done. If you guys reconcile and don't want it anymore you can rip it up. Don't file for a divorce you don't want. The post-nup will remind him that you can move forward at any time and it will be good to negotiate it while he is feeling kind toward you. If that changes or he doesn't follow-though, you will have it.
I made OD sign a post-nup 10 years ago regarding retirement. I would have paid him a huge amount of money without it. Literally the only smart decision I made with him. Don't do it yourself. The law can be odd and require lots of disclosures in this area. I made OD sign ours 4 times over multiple weeks (because he wouldn't see an attorney and I didn't want him to claim duress).
