that post pretty much describes me 5 years ago.
I can't really give you a tried and tested method on how to really overcome that, but if I had to factor it down, there'd be about 3 main points.
for starters, a group of friends that actually likes the same things you do. It's easy to feel inadequate when you hang around tanned and trained party animals. My friends share many of my interests, and we can have plenty of a good time discussing tabletop lore, videogames, science and all that stuff that is really awesome but party animals dont care about. Sex and intimacy generaly does not come up. And believe it or not, you may yet be able to find even an SO that shares the same interests, once you have overcome number 2:
your self-image. of course you can't ignore the haters when you are your own biggest hater. What I did was simple - actually change myself. I started working out, got myself fashionable clothes, get regular haircuts and started to use various skin-cleaning products religiously. I still had really bad acne with 24 ("I'm too old for that zit!"). And I can tell you, it works. Changing your outside changes your inside. It's a chore, really, but once you get used to it, it is really only about as bothersome as brushing your teeth - all a matter of getting used to, and then you barely notice it. I am serious, it feels better. Your own self-image, and the image others have of you will improve - all by your own effort.
and lastly, though that is difficult, find something you are actually good at. I studied chemistry for 4 years, cheating my way through exams somehow, and really not having a good time. It really weighs you down once you start thinking "shit, I have a GPA of 4.0 (yes, it was that bad), and some time I will have to compete with all those fucking geniuses around here for money". so I quit that shit and started to cook - and I excel at that. And that feels really good. It is good for your self-image to quit all the bullshit that you hate and actually do what you are good at - because it feels good to be good at something. Now instead of dreading chemistry lectures that bring new and complicated stuff every day, making my life only worse, I jump at every opportunity to learn more about cooking, only making my life richer. Sure, I have to get up at times of the day man was simply not meant to get up at, but that's worth it.
tl;dr don't give up man. It actually can get better.