Back in high school I felt the same way. I couldn't understand why I went out. When I didn't I felt bad and as if I was doing something very unnatural. I come from a smallish town where everyone knew each other. After awhile I got to be known as the boy who didn't go out, which hurt.
After a few years I got over it. I realized I didn't dislike going out per se, the people in the small town just weren't people I liked, we never 'clicked'. You can't like everyone and as I realized this I started going out and being with friends and doing all the stuff I had missed out on.
It's not about being an extrovert or introvert, it's more about not understanding why other people and/or yourself put certain demands on yourself when you feel like something else. Nowadays I don't care about what I 'should' do or what I'm expected to do. Not doing something like going to someones birthday party has certain implications to people, but I understand where it's coming. Now I make a choice between the consequences of my actions, not because an abstract idea of having to do something.
It's not about being an extrovert or introvert, it's more about not understanding why other people and/or yourself put certain demands on yourself when you feel like something else. Nowadays I don't care about what I 'should' do or what I'm expected to do. Not doing something like going to someones birthday party has certain implications to people, but I understand where it's coming. Now I make a choice between the consequences of my actions, not because an abstract idea of having to do something.