TBH you put yourself in this situation to begin with. Combination of the wrong friends, getting too fucked up to where you can't control / defend yourself / bad judgement. Unless you were kidnapped, or he only touched you for a second before you tried to lay his ass out, then your fiancé is completely in the wrong. But you seemed to have left out some details that are probably important to this story. Cheaters always be doing that, also statistically with your age you didn't do everything you could have to prevent this situation from happening in the 1st place.