For some context, that day was my friend's birthday party and was set in a club on a Friday. I have a boyfriend for over a year now and is okay with me going to parties without him. He trusts me to go out, but in this occasion we had lots of arguments. I was cold for a week before this we were talking but did not get the chance to talk through what happened in depth.
Few drinks in with my initial friends, I saw my friend (19M) who I met through my best friend before. We knew each other for a year now and were surprised and greeted each other. When my initial friends went to their businesses, I only knew the (19M) friend and asked him to dance in the middle along with his friends. I went back and forth between the table and dance floor to do some shots. Last thing I remember was dancing with (19M) on my back since two weirdo's keep hitting on me.
I woke up beside my boyfriend's bed and did not know what happened, I asked him on how I got there. I also asked my friends what happened to me, they said I was wondering off and keep going back to the middle and dance with (19M) friend. They placed me on the stairs and said I hung/hugged him by the neck and leaned on him. I did not remember anything beyond past the last statement I said. They also told me that I was clinging on to his neck while we were dancing (which I have no recollection of).
TL;DR My initial thought when I heard that was, did I cheat besides that I was black out drunk. How do I tell my boyfriend that I did that with no recollection?