Should i break up with my boyfriend?

last Saturday the 4th i went to a bar and i got really drunk and when i get really drunk i black out and don't know what im doing. my friend Benn unfortunately took advantage of me. we ended up going back to my apartment and you know....getting it on well about 5 minutes in my boyfriend of 3years walked in we were completely naked and still getting it on. His response obviously was very negative he cussed me out, punched my friend a few times, and broke a lot of things in the apartment. the next day i went to his house and we had a talk he said he forgave me as long as we are honest with each other from now on. later that same day my best friend Cathy of 6 years told me that she saw on facebook that my other friend Alex had been with my boyfriend the night i hooked up with benn i talked to Alex about it and she said she had been hooking up with him for over 2 months. now my question is should i break up with him or should i just act like i know nothing