how do I know if my girlfriend is cheating on me? I even took a little advice and ask her if she was and she said "no". Plz help!

You can never, ever be certain. She may be very good at hiding it; and if she wans't cheating yesterday, she may start tomorrow - if she is that kind of person. Or she may not be cheating. And you hurt yourself, her, and your relationship by being suspicious. In some ways, unfounded suspicions are more damaging than actual cheating. A cheat can apologize for the cheating, and the partner can accept the apology, and the relationship can be repaired. But from suspicion, there is no escape: it will corrode the relationship every minute of every day.

So stop looking. If she is cheating, you will probably find out sooner or later: people are not that good at keeping secrets. But if evidence doesn't present itself, don't go looking for it.

Os split up, because you are too much of a suspicious bastard ever to be in a relationship. Watch Shakespeare's Othello.

What I always do is:

NOT CARE if she's cheating. Hey you could act like a woman yourself and dig through her cell phone, check up on all of her facebook friends, start calling after her to make sure she is where she says she is, etc. Then she'll leave you for some duche who doesn't care what she does.

But if you think you can keep it together then just hack her email and use it to break into her facebook / myspace.

Unless you find proof or she admits it there is no way to know if your girlfriend is cheating. Why do you think she is?

you dont.