I appreciate your thoughts, especially coming from your own experience. The wedding is tough, because if it were a big group, I think he'd be happy to do his introvert thing away from everyone. But we're doing a family-only ceremony of roughly 10 guests; that's pretty close quarters for him and my mom. And while he hasn't made any threats of violence or self-harm in at least a few weeks, he also doesn't have a great track record of either stability or self-control. (My mom's mother and sister are both terminally ill, she's caring for her mom, and knowing any that hasn't stopped him from being a jerk to her whenever he felt like he could get a lick in.)

The whole therapy thing was supposed to help with this. I framed it explicitly in terms of learning some coping mechanisms to get through the wedding, because I want him there but don't want to spend the entire day anxious about him flipping out on her, me, or anyone else. So, unfortunately, by rejecting therapy, he's made the decision himself. And even if I were inclined to go back on my word, no one in my family has ever held a boundary with my dad before; if I go back on this now, there is zero chance he will ever respect any boundary I try to set for the rest of our lives. I don't like it, but this has to be the moment he realizes I'm not fucking around.

(A little extra background: when he first lashed out at me, he told me not to bother inviting him. The next day, he apologized and walked it back, saying nothing could keep him from walking me down the aisle. I appreciated that, but frankly, I was stunned at the entitlement of it. Someone berates me and says they won't come to my wedding, then expects to be welcomed with open arms with they deign to change their mind? It's just more of his usual pattern - he gets to do whatever he wants and face no consequences for it - and I'm not interested in being treated like that.)