My XH did this. He had all the kids for five weeks, then when they came back at the last half of summer, the first thing out of their mouths was "dad's getting married." The second was "and we're not invited." The third was my youngest saying "He's getting married on my birthday."
It took a long time for me to forgive, and even longer for them. They've forgiven, but even two decades later, they've not forgotten. This was the one thing that he and his wife did that absolutely devastated them.
Have the talk with your H. Make sure he knows the consequences.
You really should try and stress to him that he might want to rethink not having them at the wedding. H found out two days after MIL married her current H. He is still so very pissed and he was 32 when she pulled that stunt. She got pissed when he didn't call her when DS was born and he threw this in her face. It's a huge life moment, they are creating a new family unit and the kids should be there.
I don't know your ex at all, and you have always said he's a good dad, but I would bet $100M nest dollars that he is planning to be all wide eyed and say "but that was your weekend with mom," as if it was somehow your fault that he didn't have them there. That, to me, is what "they hear what they want to hear" sounds like. You're not overreacting. There are like 20 people in here saying they don't speak to their fathers anymore, in part because of exclusionary wedding practices.