How do i handle the real backstabber?

Ok this one guy (chris) who I thought was my friend called my best friend(kevin) a backstabber behind his back and he told me that I made a mistake in becoming friends with him and he said this after we got back from one of our trips which was a disaster...

since part of it had to do with my friend getting fired (he was one of the ra's) because of a rumor that he was sleeping with one of the girls who dresses like a slut. And ever since then the others have been trash talking him behind his back and acting like he's guilty when he's really innocent. So what should I do about chris because I think I'll see him during the school year and when/if I do should I go up to him and tell him off and defend kevin because he's always defended me or do I just ignore it and pretend that I don't care about him anymore?

your right I need to defend him because he's my best friend and he's always been there for me when I needed someone to talk to thank you