[neurologic]

You must see a good therapist, even if you pay out of pocket for your sessions. I am also very introverted and have also gone through a few years of loneliness, though not as intense as yours. It's fine to try and fix your problems on your own, but when you fail for several years, there is no shame in getting help from a professional. Psychotherapy has made great progress in the past 50 years with the discovery of Cognitive Behavioral Therapy. It is no longer the wishy-washy pseudoscience that it used to be. Of course, a therapist is not a magician, but it may really help. You must explore this option.

Maybe, like me, you think that seeing a therapist is shameful because it is akin to "admitting defeat". However, it sounds like you've been in an extremely difficult and painful situation for a number of years, which makes seeing a therapist not a defeat; on the contrary, it is the correct thing to do.

Good luck, I hope that you get better.