I still keep in casual contact and visit a few of them a few times a year where they are across the nation. I'm closer to my college friends though, but I've still been in some weddings of HS friends and consider my core crew basically intact. The casual friends I saw the summers at some bars back in Portland but I really didn't give a fuck about them anyways. Don't miss them at all really, just good to reconnect at christmas and summer break but eventually you just fade away from them if they don't live near you. Most of the people in your HS class you will never see again.
Don't study at the library, study at the on-campus coffee shop or dining place if they have it (outdoor if its an option). Its more relaxed. Play intramural sports. Good way to meet cool friends to party it up with during the weekends and nights...always good to have your face out there and recognizable. Don't get too worried about every last detail. Enjoy it. Try to do a study abroad program (one of my big regrets not doing this). Don't get all caught up with the drama, get as many different cliques as you can, don't get pigeonholed into one group.
I hated high school and was dying to move out of my house so missing HS itself was never a problem at all. College is fucking awesome when you first move in but eventually it reverts back into being just every day life and you get used to it (granted, still better than living under the parents unless you hate your roommates). And as for whether you'll keep in contact with your friends or not that really depends on you and your friends. The drive to my college from my hometown is only about an hour to an hour and a half so my core group of friends came down a lot and I went up to see them a lot. But I would also tell you that I didn't make any really great friends that I met in college. I have friends at college, sure, but so far none are as close as my original friends I had in HS (only two of whom actually went to my HS). It seems like most other college students I know are always hanging out with their old friends when they come back home. I think that by default when you go home for Christmas vacation, spring break, summer, etc. everyone calls up their old friends to stay in touch and have a good time.
