I feel like im a cheater

I love my bf with all my heart but I cant get over what happened. His friend always comes over (they've known each other for years) and hes always like looking at me funny I even caught him taking a pic of my ass once. I told my bf but he kinda brushed it off. Well yesterday my bf was in the shower and his friend was once again there and he...like came into our guest room when I was in there and closed the door and locked it 🫤.

I asked what was he doing he just backed me against the wall and groped my ass. I shoved him a little but im not aggressive so it was pretty much nothing to him he then sat me on the bed and took out his dick which was big tbh (something he was oh too proud about) and he told me to suck it. Ofc I said no but it was like i was frozen. He started like poking and wiping it across my lips and idk eventually I just opened up and...yea. He finished on my face. I washed it off then sat back in the living room. About 10 mins later my bf came out of the shower and we were sitting on the couch and his friend is just grinning so hard it made my stomach turn.

Idk what to do now like do I tell my bf? Is it my fault? I should've like screamed or something right? I just did it like a cheater. Idk if feel terrible and hes coming to hangout again today. The kicker? Hes gonna arrive while my bf is coming back from work so it'll be about 15 mins of us alone if I let him in.