I've gotten more skilled at group situations as I've gotten older, but more than an hour or two and I'm overwhelmed. I'll usually start to tune out quickly unless someone directly engages me. I've always preferred talking to one person at a time. The worst times in school (bullying aside, of course), were when the teacher said something like "OK, everybody break off into groups of..." That generally meant I'd become a bystander, and be miserable for the rest of the class.
When I was in college, if more than one or two people came into my dorm room, I'd basically freak out and start kicking everyone out. I just couldn't handle the social stimulus overload. My roommate laughed at my quirks. He was incredibly laid back - an absolute necessity for dealing with someone like me.