I am the same as you when it comes to friends, I always have just a small number of friends, whereas my brother always seemed to be in huge groups of people. Try ad view the positives of the kind of friends you make - they are closer, more loyal, more reliable etc, than having just a big group of acquaintances who you might never be really close to. It's just a personality thing, in my opinion, some people are more introverted and have small close groups, and others make big loose groups.
As for your housemates, that's a perfect way to meet some new people who you basically have to get along with. That's not like a threat, it's simply that, you just can't live in a house with someone and not get to know them well. As long as you're fairly friendly (ie not horrible to them - it's OK to be shy, they will be too, but just try to smile and be polite), they will get along with you perfectly well, and if you're lucky, you could make some great new friends.
I think you should try getting in touch with your uni's counsellor (most, if not all unis have one), and maybe see about having an appointment with them. They will be able to talk over your worries about making friends and such, as well as about being away from home and everything - I think it could be really beneficial to you.