Yeah, just focus on the fun you'll have there and the new people you'll meet!!
I was still my own - rather shy - self, but met LOTS of new people and had fun - maybe not as much fun as some hardcore party animal (but then again I've been called 'party animal' too he he - albeit in a bit surprised manner lol)
21 is YOUNG! My cousin went to study much later, and still had fun!!
There will be people with no friends there too, maybe even people from other countries who will probably have zero visitors too.. A girl I know worked/volunteered with them and the students' office and then later got a cool international job!! (well-paid too!) And the people who had friends or bf/gf at home will be much more homesick, usually.. May even just study and write cards home.. (that's what a roommate of mine did, though she was very nice!) You may actually have a better time there!!
For some people, high school friends or primary school friends are most important, some people actually meet people on their intellectual level at University or later.. Maybe you've just 'outgrown' people you used to know before..
And maybe later your and their interests will have changed and you'll be able to have meaningful conversations and interactions again.. People change..