For all of the "freedoms" (a great many of which really exist, and are justly celebrated) of our world today, the freedom to be alone on your own terms, to come and go from social and other situations on your own terms, not to be permanently "on", or "available" is a freedom that has been largely sacrificed. Oddly enough, our world has seen a huge erosion of the "private space", which, along with the fantastic advances of IT have helped create a world where we are supposed to be permanently available.
Our society expects that everyone will seem to be permanently happy, and affable, and willing to engage endlessly with people. Many are not, and there seems to be less space available for those who do not quite fit the "nostrum". Just think of how many job adverts seek "team players" but also someone "capable of working on their own initiative" a contradiction in terms if ever I heard one. Most people tend to be rather better at one or the other.
I'm a teacher - so, obviously, I engage with the world, I have to, and I love teaching; however, I prefer socialising in small groups, with close friends, rather than crowds, and I have a pretty high tolerance (actually a need) for some solitude on a daily basis.
Strange to relate, I was an adult before I admitted to myself that I actually loathe parties; I treat them as a distasteful aspect of "public sphere" or work-related activity, which is fine. However, the fiction that they are fun is just that, a fiction. Agree with mord's post; actually, I find myself in agreement with most of the posts on this thread. Like glocke12, I read a lot, am very interested in knowledge and learning new things. Evidently, the internet and forums such as this, suit our mental and psychological landscapes.
Cheers and good luck