You can tell for sure that your girlfriend is cheating, by catching her on the act with her lover.
Follow her
tell her.
You confront her. Tell her you know and just discuss it. Make sure she understands how you feel and do what you think is right
then he must be cheating on you if he has a girlfriend? i mean if he likes you and has a gf then he must be cheating and wanting you?
We can not know that and thus can not provide you with an answer.
be as honest and sensitive as possible and make sure that you have proof that the person was cheating
Ask her if shes cheating on you! Nah im kidding i dont know sorry ? :( and im a guy
You have to be sure that your girlfriend is a liar (lied to you before) before accusing her of cheating on you. If you have caught lying about cheating then you are wise to break up the relationship with her because once a bond of trust is broken it is difficult to go on in the relationship. Since no individual knows themselves 100% they cannot be expected to know another person 100%.
She keeps her phone and diary away from you.
cheating is doing anything you wouldnt want your wife/husband or girlfriend/boyfriend to know about
I'm not sure to be honest but if you goto him and tell him you know about him cheating and he wishes to continue to do so then he isn't worth your love and feelings. no male or female who cheats should be in a relationship.