A couple years ago a friend of mine that is still my friend slept with a girlfriend of mine. I forgave him because the girl was a slut, but now I think he might had tried to sleep with my current girlfriend now too. My girl and I were hanging out with some friends of mine, at my one buddy's mom's house. Half way through the night my girlfriend pulled me aside and told me that my friends made her uncomfortable. I played it off like it was nothing and then a couple hours later she started to beg me to have us leave, so we did. After we left she told me how he had grabbed her ass, not just once but twice and it kind of freaked her out some and that is why she wanted to leave. Two days later I confronted my friend about it and he admitted to it, but didn't see what the big deal was since my girlfriend didn't sleep with him. He said he was testing her loyalty to me for me by grabbing her. I know he is full of bullshit, but how should I handle this situation now?