I've rediscovered this about me recently. Went thru that phase again of feeling lonely, making the determination to get myself out there, then finally meeting people and joining the group. However, my new found momentum never lasts long, and after becoming progressively quieter, I return to shutting myself in again.
I simply can't keep it up. I go to a party with high hopes, talk, dance, meet people, play games, and do everything with lots of energy for a few hours. But then, there always comes a time when everything winds down people get cozy in thier little groups, and I end up becoming quiet as a mouse. I try to stick it out and even participate more, but before long I become less and less relevant and end up by myself. Once that happens, I'm pretty much seen as an outsider, and it's rare I get invited to another gathering again.
Of course, I've learned to make an excuse to leave before this downfall happens, which makes me look better.
I know I'm an introvert, and value my alone time, but is hitting this kind of rut every time common?