Problems with social life?

My best friend used to be someone I hung out with all the time. We used to party together every weekend and talk to each other about our problems. Recently, we've been drifting more and more apart. We used to playfully make fun of each other all the time but it was all in good humor. Now when we make fun of each other, its usually really heated and intense. We get in each others faces and try really hard to degrade one another. But normally, its just him making fun of me since he's alot more articulate with his words and I'm kinda intimated by that. Whenever he makes fun of me, I usually just laugh it off but try not to think about it, but whenever I make fun of him he gets all defensive and serious. The problem is, we have the same group of friends. The friends like him more now and are closer to him. It's gotten to the point where most of my friends resent me for one reason or another (my "best friend" talks behind my back and nitpicks all my flaws), and they even go out on weekends without me. I'm feeling really left out and I don't know what the problem is...Whenever I do hang out with them now, its ok without my "best friend" around cause hes not there to hate on me. But even when he is there, theres not much of a problem until he starts making fun of me and I don't know what to do because everyone just starts bashing on me. I feel so bullied, lol. This is such a little boy problem I feel so childish talking about it, but I'm actually in college haha.