I'm feeling down about this situation and need some opinions?

I've been very good friends with a guy all of summer. We would give eachother advice on our bad relationships where we were both unhappy. Eventually I broke up with my boyfriend and he got dumped by his girlfriend. We continued to talk and grew closer within a couple of months and became girlfriend and boyfriend. He is very special to me. We have only been together for about 3 months, and this is our senior year in high school. We both are going to different schools for college since he's going on a football scholarship. I can't help but look at myself asking why I'm with him when we aren't going to the same colleges and will be taking different paths for our future. It makes me sad to know that now/the rest of my senior year is probably the only time I will get to hang out with him and be with him. The year is slowly coming to an end and it seems like a countdown to when I won't be with him anymore. Why am I still in this relationship? I care about him a lot but we have different paths. Doesn't he see it too? I know he's not using me because he's fully aware I don't drink or smoke and is caring towards me.