She cheated on me =( plz help =( i dunno what to do?

You sound like a sweet person. Don't let someone like her bring you down. I know it hurts right now, but you need to stay true to yourself and detach yourself from her completely. She can't have you AND him, that's just not right. She sounds like a very selfish and troubled person, and you really just need to move on with your life and work on bettering yourself and finding someone better.