Yes, it's normal to get a little sad/reminiscent. But don't worry, if you're going to college, you're going to have a fucking blast. Just keep in touch with your friend via email and make sure you make plans ahead of time for when people are all typically home at the same time (Thanksgiving, Christmas, New Year's, etc.).
What he said. Keep in touch through myspace/facebook/e-mail while you all go your separate ways. You'll miss high school for probably 2-3 months then you don't care anymore. I've been out for 3 years and I don't miss it a bit. Especially when I'm around high school kids...
You'll be fine, bro. Just keep in touch and it'll be good. I suck at talking on the phone, so usually I lose contact with people if that's the primary way we talk (unless we see each other on a day-to-day basis).
Congrats, I also graduated, and also felt somewhat sad and reminiscent. But what kind of sucks is that I may not be able to hang out with my old buddies on breaks because I'm moving in a couple of weeks.