Tryin again... did i... did i cheat on him?

well uh yes you obviously cheated on him. clearly. and yes you need to tell him. whether or not he breaks up with you is a different story. but you need to be open and HONEST in your relationship if it's a serious one. think of it this way... if he did exactly what you did, wouldnt you want him to confess what he did that night to you? so yeha.. you need to let him know. i mean i've gotten completely shitfaced many times, but i've never cheated on my boyfriend.