From the sounds of it, I think her first story is right. She cheated and then turned the story around to get you back.

Question? How much do you do or bring to her life?

Also, do you know if this other guy is in a relationship that related to the events that happened a year ago. If so, reach out to his partner and inform them.

Either way, man. You should just cut bait and walk away from this situation. She sounds like drama. Also, learning self-respect at a young age is a powerful thing.