I think its only natural that you may feel a bond towards him, and i should hope he does to you too.
He might not be really going out with someone else, he might just make out so to wind u up or make you jealous. He could reali have a gf but that still doesnt mean that he wont have feelings for you.
Having experienced it myself, yes your old feelings for someone can return and sometimes just as if not stronger than before.
I feel sorry for you because you must hav ur heart on him to the extent u had sex wiv him, i guess even if on the surface you dnt like him deep down im sure you do...
What are your hopes ? say he does stil reali have strong feelings for you, what would you want? would you want a proper relationship with him?
Good luck!