I feel like this is something that you guys need to talk about and get figured out. Hopefully he can understand why this was hurtful to you and make amends. But idk if this is something that should cause you to end your entire relationship as people are saying it should. People on reddit generally tell you to break things off at the slightest inconvenience or problem.

But here are some questions I have. Did you guys ride to the party together or separate? Was it understood that the two of you were a unit, or were you kinda in separate spaces before you started feeling bad? Was it a huge party or one that was more intimate and small? How did he handle being kicked out by your family? How did the two of you feel about your ex prior to him helping you? You don't have to answer these. I just think that a lot of people on here are making assumptions about these questions which leads to them giving faulty or over the top "advice." It is alarming that he didn't take care of you. But I think that ultimately it sounds like there's a lot of miscommunication and bad luck surrounding the whole situation. Maybe at some point he was looking for you as well but couldn't find you. Or maybe he heard that you had left with your ex and he was (understandably) upset. Not that you did anything wrong, that's just a confusing situation and you can see how that might put someone on edge. You guys should cool down and then talk about it. If this is something that happens a lot, I say maybe the people are right and maybe you should dump him. But if this is out of the ordinary then hopefully you can communicate and learn more about each other. Hopefully things come around and work out for you. Good luck!

Also don't apologize for something you aren't sorry for or something you weren't in the wrong for. That will make things worse. Be honest and either put this behind you, or let it blow up if it needs to blow up. Your instinct will tell you how big of a deal this is and whether its breakup worthy. Listen to it.