I understand completely. I tried for years, went out of my comfort zone for what I could, tried to have friends, relationships, work. I just never felt happiness, and it started creeping on me as years passed. On the exterior I can't complain, nothing is really wrong (the partner chose someone else after years but in all honesty I understand, even if it hurts).
There is just no happiness. I slowly understood I am uncapable of feeling it. Even if I had a perfect life, I would not be able to be happy.
I am tired, too.