Do you think he likes me or no I don't understand hmm?

well I met him at the lake I started conversation with him first and I guess it turned out he goes to the same universty as me...I saw him at the gym and he approached me first and after that i saw him in the gym every once in awhile but every time i saw him he talked to me or said hi....so I decided to add him on facebook he accepted my request so one day i wrote him but he didn't write back and everytime i get on he don't write me so what do you think?