i've learned in my relationship life that if you don't tend to be overly paraniod, you tend to know when she's cheating on you. listen to your instincts, or even better test her....get a friend she don't know to try and make moves on her (not acutally doing nothing, just try to see if she gives in) if she does, then she's no good....move on, if she doesn't (and you're sure she don't know this friend) RETEST HER WITH SOMEONE ELSE, then if still a no-go she's faithful, either that or really smart.