Unfortunately you can't know unless someone tells you. But she will seem to lose interest in you and become more distant.
You can love women all you want (I do) but they are evil, don't trust them, at least not until they are in their 30's. But what the heck, dude, there is about 2 women for every one man on this planet! Surely enough to go around.
She keeps her phone and diary away from you.
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?
We can not know that and thus can not provide you with an answer.
Aboslutely, use your gut feeling most people know when the other is cheating.
Ask her if shes cheating on you! Nah im kidding i dont know sorry ? :( and im a guy
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.
if your girlfriend is out and you don't know were she is you should probibly look for evidence that shes not cheating on you
The only two ways you can know for sure if your girlfriend is cheating on you or not is by communication first. Sit down with her; face her and ask her right out if she is cheating on you. If she goes red in the face; fidgets with her hands or squirms around; stands up and threatens to leave or go into another room it is highly possible you have cornered her into confessing whether she is cheating or not. However, if you have no real proof she is cheating on you and she may not be then you risk losing her. Secondly, when she is away from you and when you think she has the opportunity to cheat on you then you can follow her one evening.
On a holiday, you would want to spend time with your girlfriend. And if she is cheating, she'll refuse to show up. That is one way to find out. Also, her weird reasons for not doing what you usually do, can imply that she is cheating.