I was at a party last night, and my friend and I were both interested in the same girl. I ended up kissing her and stopped us after just the kissing. However, today I found out that he has had sex with her multiple times and I don't if he has any hard feelings torwards me now. Before, I saw it as just a game between us to see who could get the chick but I didn't know that they had done anything. What should I do?