For context, I am dorming with my best friend and this is our first year in college. At the beginning of our first semester he ended up sleeping with a girl that is in our friend group, while still in a long distance relationship with his current girlfriend that he had from highschool. I figured out through friends that he cheated on her and told him that he should tell her because if he truly loved her he would not cheat. I also know his gf because we all went to the same highschool together and we are all friends. Anyways, I wanted to tell her immediately when I heard that he cheated but I was worried how it would have an effect on his school life and mental health because he does not take break up's easy. Now to present times in this late second semester of college, he decides while drunk to text the same girl that he slept with some suggestive texts that seem like he wanted to do something with her. I feel so much guilt because we have all been lying to this poor girl that is being played with by a guy who claims to love her. So I decided to confirm her suspicions that she once had and tell her that he did sleep with someone else while they were in a relationship. I know he hates me for it which is the only reason I feel bad. It is a wierd pity that I feel for him. Even though he is not the victim, I don't want to ruin anyone's lives. He has already texted me saying he wants to take his stuff out the dorm and live with a friend near campus, so I know he has some resentment from me. Also for further context, they have been dating/been in a relationship for eight months, and he told me that she knew that he cheated (which I didn't believe at all).