Kissing a girlfriend drunk at a club?

What do you think? My friends and I were at the club we were wasted acting crazy and my best friend kissed me and we made out for 5 seconds and laughed about it it didn't mean anything we were just acting crazy. Well my boyfriend found out and he's pissed he said it doesn't matter what gender it is kissing someone that isn't him is cheating. I don't understand what's the big deal I don't want to be sexually with my friend I think he's blowing it up and it shouldn't be a big deal what's your take on it?