As for what happened in our conversation with the H.....You got the reality slap. While you two were living the quasi family setup, you weren't grasping 100% of the current situation. Your H then showed you the current reality in that he is looking for his own place....and has one lined up. You responded excellent to this admission too....You removed motion...Listened...validated....and had a productive conversation instead of an emotional charged brouhaha.
Good Job 3B....Way to go!!!
One word of caution....Live in the present and don't predict the future.
I suggest reviewing your boundaries in light of the current situation. Family Sundays seems fun, but what concerns me is that your H is not going to show the kids his place. I feel that may be some sort of overt manipulation to keep seeing the kids in the house instead of taking them somewhere. Your H sounds like an excellent father, but 3 boys is one heck of a load to handle on his own (Honestly I am totally impressed how easily you seem to handle it). I think a very good step in his growth would be handling the boys on his own outside of the house.....a reality slap of his own. Think about that one!
You are doing great 3B.....I see you making substantial life changes and you get a pat on the back from me for that