A lot of people do their own thing. They have their own way of going about their days and would rather stick to that than venture out or change. For some people, a big part of having a good day is finding, more often than not making, time to be alone.
It's in my personality to love my time. Time to myself in quiet or with my music or watching my shows or something as small as painting my nails. I need this time everyday but I'd be fine too going day after day without any contact with anyone.
College actually makes it pretty easy to do this. I could camp out in the library all day in my own study corner with vending-machine snacks and printer paper on hand. I could lock my apartment room door, put on Netflix, surround myself with anatomy notes, and not come out for 72 hours. Some may say boring, I'd say ideal.
College, however, also makes it very probable that you'll have these fabulous friends that both pry you out of your room or join you in your bean-bag-library-study-spot. These friends are the best part of college. You get to go to dinner with them, go out, do everything fun, and experience it all with them. They're the ones like you see in the movies that sit on the couch, talk about weddings, and eat popcorn, cookies, and What-a-burger all in one night with.
The rather fantastic part of these fabulous friends is that they are like you in more ways than one. You see, when you go to college, at some point you realize you only have to do what you want to do, you only have to be friends with who you want to be friends with. And as you're making these friends, the friends you choose to make, you typically vibe with them because they're like you in at least three ways.
That's how you keep friends when you like being alone. You find people that like being alone too or you find people that give you that time to yourself. But even better than that, you have to find those friends that fill your time and make you happy when you're not alone. The people that make you want to leave your bed and go do fun stuff with. They're the ones that make you get out but let you go home, too. They're the ones you're friends with when you could be friends with anyone, They're the ones you do stuff with when you can do anything you want,
There's nothing wrong with being an introvert sometimes and an extrovert other times. You can hang out with people and still spend time alone, and enjoy both. Of course it's a balance, everything is. Find your people, the ones that understand you need and want to spend time alone but also the ones that pull you out every once in awhile.