A boy

So, there's this boy who's 3 years older than me. He started saying hello everytime he saw me in the hall and after a month he stopped. We had 3 ''closer'' encounters, once he even barged into the classroom I was in and actually put his hand on my chin and raised my head towards him. I sorta fell for him. He stopped talking to me after a month. I sent 2 anonymous letters to him. Also, I added him on facebook and tried talking to him, but he didn't seem interested. I don't know what happened. He is 18 and may think I'm just a kid, or maybe he just lost interest. Anyway, he is leaving school this year and I'll probably miss him and feel bad I didn't try more. I don't to bore him, what should I do?