Found out SO cheated on me 😭

It was true. I posted awhile ago about my SO having a receipt to a hotel room with his ex’s name on it. My friend and I acted like someone they knew from high school. She told her that she doesn’t regret what she did knowing it was wrong. I don’t know what to do. LEAVE. Yes. But how do I bring it up to him? I don’t know what to fucking do. He’s at my house now sooo. Suggestions would be helpful for sure. Idk how to come up with what I want to say. It hurts but doesn’t bc I had a feeling something happened. But knowing now makes me feel so fucking numb 😭