I second having roommates. I'm terrible at meeting new friends but have pretty substantial social networks stemming from random roommates off of Craigslist. The best man at my wedding was a Craigslist roommate, who was very much a social connector. Much of my social network when I moved to another city was from his college friends, and another group here was another roommate from Craigslist's friends.

Look for good roommates. The more social the better. I also was similarly uncomfortable with roommates, commuted to college, lived alone, and one day in my early 20's I made a choice to deliberately do things that make me uncomfortable and it changed my life forever.

Step out of your comfort zone. Its the only thing that will change your situation.