Why are guys in frats so crazy?

I've been in love with this one guy since my freshman year of high school. I'm in college now and so is he. He is in a fraternity and drinks, parties, smokes, sleeps around, etc. These girls write nasty stuff on his MySpace, etc. We still see each other from time to time and sometime I think he is maturing or the feeling is mutual and then he just acts so dumb and immature. Just reckless.