F.B.
I saw this kind of thing on Super Nanny. This is what she did to help the parents break their child of this.
First thing to do is to get your son's bed back into his own room.
Since your son is dependent on you being right next to the bed for him to fall asleep, you need to work on getting yourself out of the room. First, place him in bed and sit on the floor with your back to him. If he cries, let him. When he calms down, slowly move closer to the door keeping your back to him. Do not turn around to look at him. If he sees your face, he will start crying again. If he does start crying when you move further away from him, do not move back. Just let him cry it out. If he gets out of bed, pick him up and put him back in bed without saying anything to him. Once you are out of his room and sleeping in your own bed, I am sure that he will still get out of bed. Every time he does this, take him back to his own bed without saying anything to him.
I have seen this work on the show and know some parents who have used this method. It does work. It won't happen overnight. But you will lose much less sleep by breaking him of this dependency than you will by continuing the way you are now.
Good Luck!