Leaving my long distance boyfriend, need some advice

I'm actually so upset right now, I don't even know what to do. I've been with my boyfriend for a year and a half and we're both 17, and for some reason I've never been this upset about leaving him. We only live 3 hours away, but it's really hard since we're still in high school. I was supposed to be seeing him tonight for the last time (we've been hanging out for 3 days now) but something came up and now he can't, and I just feel absolutely miserable. It really hurts that I can't say goodbye to him, and I probably won't see him for another 4/5 months now. Does anyone have some advice on how to feel better? I've been crying for like a half an hour and I still don't feel any better at all, I'm going to miss him so much :(