Fiance is mad at me for no reason,please help?

There's these 3 guys I used to see(friends with benefits)we met 3 years ago. they all worked together(marines). I met my fiance 2 years ago and ended all contact with the 3 guys. Things were going great until he joined this semi pro football league and it just so happens that the 3 guys are on it too. When they realized I was with my fiance they started treating him real bad so I admit that I slept with them before I even met him. He was mad and said that he doesn't want to talk to me for a while, I just don't get why he's mad at the past. I'm not mad at his past girls. I'm so confused???