Thank you for the description of avoidant personality types, I recognise elements of this in myself.
Similar themes were explored in the anime Neon Genesis Evangelion. I would suggest the main protagonist Shinji definitely has these traits (probably expressed mostly directly through the 'Hedgehog's Dilemma'). I felt a certain amount of relief after finding that show, that at least the creators understood. It also helped that it was a great anime.
To be honest, whilst I don't have the same desire for friendship that I once did, the main thing I do have desire for is a form of sensuality (not sexuality). Moments that are complete without words/with very few words. That's not exactly the easiest thing to communicate to other people, so most of the time I'll just enjoy it in my own time.
When it comes to activities, I'm not short of options. There are new things I want to try, and things I've already enjoyed. What I find less easy is to enjoy them with other people. For example, whilst I've danced with partners before, I tend to prefer dancing by myself. I'm very happy just closing my eyes and letting my body move to the music.
I don't think this is a "forever" state as you put it, but I think this is why some people suffer for so long (some researchers call this chronic loneliness [0]), and turn to fantasizing friendships as a way to cope.
I want to believe there's a way out, I'm not certain, but I think therapy and mindfulness could help, and also being around secure/empathetic people. Loneliness is kicked around as the bastard child of psychology and most practitioners will disregard a lonely person as simply depressed.
But taken to an extreme, according to attachment theory, there is a class of people who naturally gravitate to social isolation yet, paradoxically, desire closeness -- they're called avoidant personality types [1]. There is early research (Bowlby, Ainsworth, lots to read online) that trace the development of this behavior to experiences as an infant. I think these types of people could get stuck in their ways through their 30s and 40s.
[0] http://magazine.uchicago.edu/1012/features/the-nature-of-lon...
[1] https://www.reddit.com/r/AvPD/