T, why not just be straightforward instead of searching for a passive way to make him not go? There's no need to try to engineer an "oops". There is an option where you just tell him he's not coming.
If he seems like he's making arrangements to accompany you, just calmly say "H, I think it's best if you don't go with us."
He might get emotional, and that's fine. If he does, you can briefly explain "H, you chose to leave the marriage. That's your choice. But now you seem to want to dictate what life looks like after you made your choice, but I get choices now, too. And I just don't share your vision that there will still be family events that include you after you've left. That doesn't feel right to me, and so I'd like some healthy boundaries in place instead. You are always free to have your own events that include the boys, though!"
If he tries to pull you into a R talk, hold up your hand and say "H, I'm not interested. I've heard it all before, many maaaany times. I'm not arguing about your choice. I am simply requesting that you to respect my choice, too."
Be calm and collected. Do not get emotional, but you don't need to be angry/mean.
You are not being mean to H. You don't have to worry about how he feels about missing out. He's an adult, and if he wanted to have family events, then he shouldn't have left the M. It's really as simple as that. He doesn't get to leave and have you shield him from feeling any loss.
He may demand his ticket and travel separately. If that's the case, I wouldn't turn him down. I'd just give him his ticket, due to the circumstances.
(In this reply, I gave you the instruction manual version of advocating for yourself because I know you still crave details. You can do what you want, but I wanted to give you a plan based on how he might react because I know you still doubt yourself and crave specifics )
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