Girlfriend and ex boyfriend?

So here is the thing, my girlfriend and i have been dating for almost a year now and we love each other very much, here is the thing though. When we first started dating, her parents were going through a divorce and idk if this effected any of the things she did to me or not. The first thing she did was comment on her ex bfs little brothers picture stating "you look just like your brother" a month after she goes to a party were he is there and supposedly he follows her arpund and continues to grab her and grind all over her, she says they did not dance but there is pictures of both of them smiling and him grinding on her so i find that hard to believe. 2 months later after that supposedly her friend and her had "a bet and a joke" that she would wear his jersey and took another picture with him this time with his hand around her hip. Another thing, 2 days after we started dating she went to the lake with a bunch of guys that like her which i think is disrespectful. All of this pisses me off because she knows i hate him and cant even stand hearing his name so idk why she would do this. All of this was done with the same ex boyfriend so im just really confused. She says shes not the same girl now and she loves me and shes changed, but idk if i can get over all of the stuff she has done to hurt me. Im justs uper confused, i cant let her go to save my life because i love her so much. Can you guys help me please because no matter how much i think about it i cant figure out what to do.