My bf kissed a boy

Hi!!! I don’t know how to put this but… My (18 F) boyfriend (18 M) kissed a boy on NYE. Early in our relationship I told him I think kissing anyone other than your SO is cheating, even if it’s a boy (in his case). Throughout the relationship (1 y and almost 6 months) he kissed a few boys when he was drunk. I looked past it since we had other problems in our relationship, but it always bugged me. He kept telling me that it’s technically not cheating bcs he’s not attracted to men. This why I’m writing here: half an hour ago we were talking about random stuff and he sent me a video of him and his best friend kissing that night (it was a short kiss and they told another friend of theirs happy new years). It dawned on me that I shouldn’t have looked past it and that it was rlly dumb of me to ignore it. I told him it was cheating and we went back and forth on this topic, then he told me to post it on reddit to see what other people think. I feel like I need to say that I support 100% everyone and I would support him too if he came out, but am I overreacting? Is it normal for guys to kiss each other? Should I be concerned? Is he right and it’s technically not cheating? How do I go from here?