Caught in the Act

I was studying late one night when my roommate's boyfriend came over unexpectedly. We were already pretty drunk from a party earlier, and before I knew it, we were kissing on the couch. She left to make us drinks, but we didn't stop there, her boyfriend took me right then, thrusting into me hard against the cold leather while she was away. It felt wild and taboo. Should I tell her? Is this something others have experienced too?