ESPECIALLY the first paragraph. WTF does he think your blessing would do? Make him feel better? What about your feelings, and how objectively insane his entire fantasy is?
I think it's OK to give yourself time to grieve about things that are gone or possibilities that appear gone right now. I think Scout's advice is dead on re: canned responses and stop engaging. He probably continues to bring it up to get your almighty blessing for his idiocy, and is only thinking about his feelings under the veiled excuse that it needs to be joint. He didn't make all the decisions up until now as joint decisions, so why now?
Continue to focus on enforcing your boundaries. You are a strong amazing lady. Hugs to you