I wish I could say something helpful, but I feel the same way. Only without all those cool activities and social life. Every year it seems I'm spending more and more time at home, not doing anything and feeling sorry for myself. It's like I already gave up.
Still, there are friends and acquaintances who support me (sometimes in a not-so-friendly manner, but I know they mean well and want to help me feel better, or at least I hope so), and that's a very important thing. One of them even convinced me to start going to the gym with him next month, even though I used to think it was futile. But fuck it, it's my life and I'm gonna do it anyway! Now it's a matter of finding more outdoor activities, and forcing myself to do the things I like but stopped doing, like playing bass (still need to learn quite a lot) and writing shitty songs, plus maybe learning some more programming languages in order to change jobs in the future.
So I don't know, maybe it's not really about feeling happy, but about doing the things you enjoy and discovering what you like. Keeping yourself busy and everything. Having a good time with your friends, be it at a bar or playing Mario Kart in someone's house. As for finding a SO, I have no idea, that's something I'm 100% confident will never happen to me. But if you keep doing all those interesting things (and yes, they are interesting, even if it's hard to realize it), chances are you'll find someone eventually. It's great that you have the motivation to do all those things, and I hope you never lose it. That's something amazing indeed.