you're not alone and I do understand.
last year, my younger sister got married. it was held in a city three hours away. rehearsal was Thursday night, off on Friday, and Saturday was the wedding (pics at 4pm and ceremony at 6pm). I was at an outdoor music festival Thursday and Friday, by myself. without that 'me' time, I would have never made it through.
I spent the first night at my other sister's house, and my parents stayed there too. the second night, I stayed in a hotel room with my parents (to save on costs). by the time the reception was over at like 11pm-ish Saturday night, I was completely ready to get the h*** out of there. even though that meant I wouldn't get back until like 3am!!
my parents (and sister) kept asking if I was staying for the gift opening sunday morning and it hurt me that they kept on badgering me about it. but I had to leave, couldn't explain it any other way. I was sooo messed up that for like the first half-an-hour to an hour of the trip, I cried! and I haven't cried in many months.
but I was there at the wedding & wedding-related activites, and I was smiling and doing small talk with random people here and there, and even helped out with my 2 yo niece. but just like you said, you require that alone time!
and just like you mentioned, I have wondered what it would be like to actually have friends / a social life (maybe even a byfnd), to be happy around others, to actually enjoy it instead of it being an affliction (or something like that).
my grandmother is 96 years old. and I have a few times apologized to her, saying I'm sorry that she won't be at my wedding! she probably thinks I'm joking, but I totally serious.