Hi Class...
I totally understand what you're saying. I'm in a similar position, but more like I have no friends because, unlike you, I didn't manage to keep in touch with old friends like you did so well. Maybe you haven't made the wrong choices afterall. Sometimes some people simply move on, and what used to be, isn't anymore...
You have innumerable options and plenty of new choices to be made ahead of you. You seem to be someone with a rather active social life. Believe me, some people don't do half of the things you do, hon. Take your time and try out new things. What are your hobbies, for instance? Let's say you enjoy amateur photography, painting, etc. Whatever they are, you can sign up for a class or something and you'll definitely meet new people who will have at least that in common, which is a great start. Plus, this roommate of yours... You can try hanging out with her and her friends for a change. You might meet someone that is your roommate's friend's friend, that is looking for a friend too. It's all a part of networking my dear...
Another thing too. Maybe this "not being able to make new friends" thing lies within you. I've got a bit of that... People are just different at some point in time in their lives. Like me. I used to have a sh*t load of friends. Always have had that groupy thing up until a few years ago, when I started dating someone (a-ha! It does impact one's social/interpersonal life afterall...) and drove my friends away... Now, that I'm single again, it's hard for me to imagine myself being that goofy-and-full-of-people-around-all-the-time type of girl just because I haven't been that way in so long. But if it's within me, than it'll eventually come to a turn around and I'll be having friends over all the time in no time. Or maybe not... Who knows?
Do one thing though. Avoid the feeling unhappy thing just because you don't have as many friends, or THE friends that you wish you had... It ain't worth it, and it is probably an unrealistic feeling of sadness... There's gotta be something else that bugs you other than this that might be accentuating it. Enjoy this "free time" (I'm guessing you spend quite some time alone) to nurture yourself and find out the things that you trully enjoy and oughtta be doing... New friends will come along and the ones that really matter will stick with you no matter.
All right, all right... Enough with the shrink talk...