AIO for my boyfriend, kissing another girl in a random game

ok honestly I don’t think I’m being dramatic but he keeps calling me dramatic for this and saying that I shouldn’t break up with him over this dumb thing, but I just need to show him that I’m not crazy. So basically we were at a party and everyone was playing like this random game and he got asked to kiss the prettiest girl. and everyone was like he’s gonna pick me his girlfriend and no he kissed a random girl at the party. Literally in front of everyone and it wasn’t just a little peck it was like a full on make out and I was sitting right there. so when we left, I told him that made me really uncomfortable and he said stop being so dramatic. So I don’t know but I made this account just to ask people their opinions. Do you think I should break up with him or should I just get over it? I really don’t think I’m being dramatic but also at the same time he keeps telling me it wasn’t that deep