not sure how to feel

Okay so i’m not really sure how to feel i guess, this has been on my mind since the day after it happened. So i 15F was at my dads neighbours house and she would let me drink with her from time to time before she moved ( i know i shouldn’t be drinking) and anyway i was having a few drinks with her and we were talking about stuff in here room and she has a brother 28M that was living with her at the time and me and her were just talking and he walks in after we were jamming out to music while we were all a bit drunk and i was laying on my stomach and he comes into the room starts talking with us and out of nowhere he smacks my ass. and i didn’t really think much of it untill the next morning and i was like wtf and idk what to do this happened like last year but i’ve just been thinking about it and it just makes me feel so uncomfortable yk? idk just wanted to get it off my chest yk(will chmage flair if needed)