Girlfriend and friend Issues

[AcesUp2121]

I've been with my girlfriend for 7 months. We broke up on Wednesday, and got back together the following day. Yesterday, I receive a call from a guy I play basketball with. He tells me he needs to talk to me. I meet up with him and he says that my girlfriend has been contacting him non stop this week and that they have hung out twice, but nothing has happened. He also said he could have hit it if he wanted to but didn't out of respect for me. He claims that she told everyone we had broken up at the beginning of the week. She then proceeded to hang out with him and a group of other people that I know. He says they all can corroborate his story but I have yet to contact them.
When confronting the girlfriend about this, she adamantly denied it. She admits to hanging out with him but it was in an effort to obtain information on me regarding a rumor circulating that I cheated on her on a recent vacation. She says he has been initiating the contact, talking bad about me, saying she can do better, etc. I relayed his story to her and she gets furious and wants to file a harassment report with the cops against him. She says she can get a print out of the text messages she has received from him. I don't know how possible this is.
What is my play here? I've known this dude for a number of years, always had respect for him, and considered him a standup guy that would never do something like this. My girlfriend is pretty hot however (pics later perhaps) and who knows how strong the power of the pussy was. I would consider us friendly with one another but not the closest of friends. We only really hang out when we play ball. My friends are all inclined to believe this dude. His story has more specifics to it then hers does. Perhaps I'm just blinded by this girl though and want to somehow believe her.
Regardless this relationship is probably over. I just want to know the whole truth. The fact that my friend hung out with her is [censored] up as it is, but if he was coming on to her and talking [censored] about me then that is a whole other story. He's bigger than me and would probably beat my ass but I would still jack him in the face repeatedly until I couldn't lift my arms.

Comments/Suggestions?