The solution I see here is for you to write a note, perhaps call her on the phone, and explain that you don't believe whatever rumors your friends told you, and that even though you hold no harsh feelings against her, but you think it is best to just go your seperate ways. Ignoring her will make her think you are still extremely upset with her, but talking for too long about too many topics will make her think you still want to be with her. The conversation (if you decide to have it) should only be a minute or two. Say your piece and leave, simple as that.