My boyfriend's best friend is like a brother to me and he's leaving to Chicago for college? Help plz!?

We were friends for a while, and later we had some conflicts and at one point I even kind of hated him, but he became like an older brother to me. His girlfriend lives in Chicago and he's going to college there to be with her, and we live in California! I've known him for a year and a half, and he's a like brother to my boyfriend and to me, and the last one of his friends I still felt a fondness for. I don't know if I'll be able to see him again, and we have almost no contact. We're not on really good terms right now, but how can I show him I'm mature and can be a good person again? I don't want to cry and seem pathetic. He's 18 and a senior like my boyfriend.