I NEED TO KNOW!!!!!!!! :(?

Okay I was dating a guy over the summer that left on a two year LDS mission right before he left he talked to me less and less I told him I could tell he didn't want a girl friend before he left he finally agreed so we went to being friends after this he it was a rare thing for him to talk to me when he left three weeks later i went to his farewell and he would glance at me then sharply look away after he was gone. I wrote him few letters and received letters back well then i stopped getting letters! his best friend and one of my best friends said that he still asks about me all the time! I guess me question is why did he stop writing me? Should i suck it up and write him again and see if i get a response? Does he even care? He left in October so has been gone about six months. I'm not allowed to call him or any thing like that just letters.