I really a like a guy a lot and he likes me too. We have been talking with one another. He always compliments me and is always there for me. He told me that he does not have a girlfriend. But one of my friend chatted with him on Facebook and he told her that he has a girlfriend and they are together since one year. He does not know that it was friend to whom he said all these. I am very confused. I don't know what should I do. Why did he lie to me in particular ? I never lied him. Please help me. Tell me what should I do??

He may have though this girl was interested in him since she was asking about a girlfriend, perhaps he made one up so this girl would not be interested.

But this sounds very 12 or 14 year old, in real relationship friends don't go behind your or his back and do this ( what if he and this girl had hit it off and they became a couple?

Honesty, so ask him

Maybe he lied to you because he likes you. Maybe he lied to your friend because he doesn't like her. But what ever the reason, if he does have a girl friend, you need to leave him alone. He's a liar and would be a cheater.
Ask him!