I don't fit in to normal society, but there are places where I do fit in.

I fitted in with the smart kids at school, with the serious students at university, with the technical people at work, with gamers. There was even a therapy group where I fitted.

I feel at home among the SIs, DIDs and GIDs on the psychotherapy forum here.

When you are depressed, everything seems absolute. "I don't fit in anywhere. No one cares. I'm no good at anything. I''m never going to be happy. Nothing good ever happens to me."

You might want to write down and keep: the one place you did fit in, the one person who did care, the one thing you are good at, etc. Even if you have to go back into your past to find them, they will be a comfort to you. What's happened before can happen again, right? If one good thing happened, there should be others.