Don't get defensive. This is not a criticism. Just an observation.
It seems to me that people have what I like to call a "Companionship Quota". This is basically the amount of time you need to be around companions. By companions I mean people you talk to as a friend, people you confide in. vs say fellow students in your class or co−workers that you really don't talk to that much.
What's the point? The point is if you haven't met your "Companionship Quota" you aren't happy. You're lonely, you feel something is missing etc.
If you have met your quota then you find that you don't need to contact others. Your need to talk and confide is fullfilled.
Generally through my own choices I'm usually in a situation where my quota is not fulfilled. For example I moved to Balitmore, I moved to San Fransisco, I moved to back to California, I moved to Japan etc.. Each time removing myself from the people I confide in and therefore unable to reach my quota.
On top of that I'd say my quota is very high. Whether that's something that happened in childhood or something that happened as a result of usually not meeting my quota I'm not sure.
You probably all notice you get more mail from me when I'm in Japan than when I'm in California. That's because my quota is not met and so to try to fullfil it I write lots of e−mail. When I get back to California you will likely see it drop off sharply. For some of you it will be because I'll actually talk to you face to face. For others though it will be because my quota has been reached and so I won't feel the need to communicate like I do now.
The same thing happens when people get girlfriends. Their quota is quickly met and so they don't need to contact their other friends nearly as much.
It's also interesting for me to note that I know people that have never once in their life lived alone and therefore have probably never experienced not meeting their quota. I'm sure there is an opposite syndrome though. A "Companionship Threshold". The point at which you NEED to be alone.