So I started talking to this guy & we started dating at the beginning of the semester.
He lives at a fraternity house & I'm very good friends with all the brothers. I think we broke up because he's jealous that I hang out with the other guys also when he's not at the house, is that so bad? They all really like when I'm there.
I talked to a lot of the brothers and they said they don't believe he ever really had a "serious" relationship before.
He never really has given a straight answer about anything,
He's not a very open person.
I really still like him, and would like to know what I could do to get him back,
Or even become close again.

Hanging out with all the guys gives an impression that you are available.
Guys don't feel comfortable with having the guys around their girlfriends when they aren't there. When the guys are talking,among themselves, they are talking about their conquests with girls. They get pretty graphic. I remember the fraternity scene, it can't have changed all that much.