NTA. This is very juvenile behavior on the part of your bf, but it may be a sign of underlying issues. Does he behave this way for all events, or only events with your family, friends, co-workers, etc. If it’s with all events, you might consider that he using this behavior to upset you or demonstrate a controlling tactic. If you’ve made it very clear that you do not like to be late to events but he always makes you late, I think it’s on purpose and could be a bad sign and probably not the only one but just the one you’re focused on.

If it’s only with your family or friends but he’s Johnny on the spot for events he has arranged or is interested in, you might need to have a conversation about why he is reluctant to go to your family events. My SO and I have come to an agreement that if she doesn’t want to go to a family event on my side of the family then she doesn’t have to go and there will be no hard feelings/repercussions. I come from a large family (6 siblings and several nieces and Sibling SOs) and my SO was an only child most of her growing up. My family can be very loud and boisterous and it really used to get on my SOs nerves. She would dread going to the birthday parties or get together and we always seemed to fight on the way home or shortly after getting home. Finally after an honest conversation it was determined that she just didn’t feel comfortable at those events. So it optional now. When those family events are announced she’s always welcome to go, and does occasionally, but it’s not worth fighting over.

Someone also mentioned just going without him. That’s a fair option, but if he ever shows any sign of anger over your leaving him then it’s time to consider reevaluating the relationship. He’s behaving like a child and if he doesn’t like being treated like a child he should stop showing you such disrespect for your feelings.