What's her problem. i'm the one guy that DOESN'T cheat on her and she breaks up with me?

i would never cheat on her. i have no reason to cheat on her. but the group she hangs with has been telling her i'm a cheater blah blah blah. they don't even know me. and she says " i'm too good looking to be faithful". she also said i'm too nice and that's apparently that's a sign of a player. My girlfriend is beautiful but i TRUST her. i'm not the jealous type. A lot of girls wanted me but i chose to be with her, and this is how she treats me.. by sending me a nasty break up message on facebook cursing me out along the way. She told me every relationship she's ever been in the guy has either cheated on her or pressured for sex. i have not once pressured her for sex. i told her whenever she's ready because i would never ruin a good thing like that. i care deeply for her.. We were dating for 3 months. I even gave her my mother's ring because i thought she was special to me... my brother was buried with an identical ring. I'm 24 and my girlfriend who is now my ex just turned 19