There are signs. If she seems distant from you, and just generally different its a possibility. If there is a new guy in her life that she constantly talks about or talks to, that could be a sign too. You could always come straight out and ask her, but don't accuse her. Don't make her feel like you don't trust her, but let her know your worried. It's really hard to tell without actual evidence.
Follow her
tell her.
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?
if you want to know that your boyfriends are cheating hear them lieing if they telling the truth and they are not cheating just forgive them or because they see other hottest girls and they probably got a little crush on them but don't do that on your girlfriend if you have one if you want your own family
We can not know that and thus can not provide you with an answer.
If its a rumor going around that you are cheating on her why dont you tell her that its not true and she cant belive everything that she hears and she needs to trust you and if you really love her and she knows it than she will know that you are telling the truth.
Ask her if shes cheating on you! Nah im kidding i dont know sorry ? :( and im a guy
Not telling just stop cheating
If you did not cheat then tell her to show you the proof. There cannot be any proof if you are telling the truth.
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
Sweetheart, if you who know who she is and possibly lives with her don't know, we certainly do not.