My(24F) boyfriend(25M) hooked up with someone after breaking up with me and then got back together with me on the very same day

So my boyfriend and I have been having a lot of trouble for a while and we keep breaking up and getting back together. Technically we are sorta broken up right now too. Recently, we were finally able to make some progress. I saw some hope for us and then he told me about this hookup. It happened after one of our fights and he says he hated it and just wanted to get back at me. But he has always had this pattern of going on dating apps after we "breakup".

He gets very mad when I say he cheated on me. He says he agrees what he did was wrong but he wouldn't call it cheating.

What is the right way to deal with this situation?