relationship help

I'm going to college next year and my boyfriend will still have a year left of high school when I go. Both him and myself are worried about what is going to happen between us because we have been together for almost 3 years and do a lot together. I don't know what to expect or what to tell him. Every time it gets brought up we both get very upset and end up crying. And he gets really upset and I don't know how to make him feel better about it, he tells me he doesn't want to hold me back and wants me to have fun but he's worried I'll leave him and says he doesn't know what he'll do without me being around. And I feel the same about him and worry that he won't want to stay with me since I will be gone and won't get to see him a lot. I just was asking for advice on what to tell him and how to help us get through this because we both want to be together in the future.