Once you've decided that you actually want to go to, say, a weekly meeting, but you only manage to get there once a month or so because it's just easier to sit in your room alone, you can find ways around the lack of motivation.
-Find somebody in the group who lives near your dorm (or at least has to walk by your dorm on their way) and have them stop by and pick you up to walk together.
-Arrange to meet somebody in the group for dinner right before the meeting (bonus: you get to develop a relationship with this person).
-Mention to somebody in the group that you'll see them at the meeting, that way you have to show up in order to keep your word.
-Tell somebody in the group that you're having trouble pulling yourself away from your work to come to meetings, and ask if they'd be able to call you 15 minutes before they start to remind you to come (and perhaps persuade...).
-Spend the afternoon in the library, then stop by the meeting on the way back to your dorm room. If you're not already at home, then you've got to get up and go sometime. Might as well go to the meeting.
I can definitely understand your position. There are lots of times when I would much rather just stay home than deal with getting myself together, going out, dealing with people, and then coming back home. But unless I'm truly exhausted and overstimulated, I usually have a good time once I get there. And I remind myself that I've always got the option to leave if it doesn't work out. If I get up and go to a party and it's just too much, I can always excuse myself after an hour and say that I've got to do something, or that I've just had enough and I need some quiet time.
I usually end up using the technique of scheduling all of my stuff in a row so that I don't go home in the middle of the day. That way, I don't have to worry about getting the motivation to go back out. I'm also generally expected to show up at several things, because I have been coming regularly for some time. So if I don't come, somebody will ask where I was. Which is further motivation to go.
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I don't do small talk.