Difficult friend question?

A few years ago I met these two friends of mine at this group meeting. On of them was totally cool and everyone knew him and the other not many people knew and wasn't very involved in the group culture because he thought it was cliquey. Their names will be George and Karl respectively. I came into the group and rose almost immediately in popularity by being invited by other friends. I am not a very experienced person in life (still having trouble coming out of my shell). We got together and were going to go on a triple date but I got nervous and me and George sort of turned on Karl part because I was nervous but also because George had some other problems with him. Karl flipped out and stopped hanging with us for a short time. He returned later during the summer to rejoin and ended up causing me to leave because I didn't want to move in with him since I was still in school at that time. He flipped which was the main reason I left.

Everyone in my group can't stand this kid (Karl) but standing up to him is impossible for everyone in the group (including George) since he has had a rough upbringing. It is to the point with me where when he is around I feel sick to my stomach and tend to just naturally leave him out because he acts so miserable.

I have questioned whether to be his friend or move on. Whether I should come out of my shell since I feel like it would help me. His idea of that seems to be almost losing myself. Now I feel like the bad guy too because I feel guilty about everything I don't do for this kid (Karl). I also feel like I am caught in a routine and no on really wants to do what I want to do.