I had dated this guy for a year, at first, our relationship was so good that everybody envied us.we lived together for a year. Then things started going bad and next thing I knew that he started seeing his friend's girlfriend. They have been together for three years now! It shattered my life, my heart got broken and at first whenever I asked him he denied seeing her.but then later I came to know that he was with her.I tried dating other people but I couldn't do it. He calls me sometimes and we meet at times.we have been intimate a couple of times. I still have feelings for him, and I don't know what to do.at times when we talk, he says he still feels something for me.please help me!I feel so confused and so lonely.

Why is this under Teens? You can't possibly be a teen?
The only way to get over this is to cease all communication. He's having it both ways and it isn't fair to you. It would be rare if he decided to get back with you after 3 years. He might on a rebound, but something drove you two apart when you did break up, and you have to remember what that was.

You need to leave him alone. He is cheating on her like he cheated on you.
You said you dated this guy for a year and lived with him for a year. Maybe you jumped into this thing way to fast, before you even got to know him.
He does not sound like a very nice guy. Stay away from him. That is how you'll get over him.