Something a bit like this happened with me. Apparently we did get an autism diagnosis sometime when I was a younger child, but we didn’t ultimately do much with that. I ended up in a social group or two in school for a little while, but they sucked and I eventually left them and we kind of just forgot about it. Fast forward to grad school when I burned out and got diagnosed with pretty severe depression and it came up again that I was autistic and that at least some of the depression probably came from the frustration that comes from the friction between my differences and society. It got so bad that I dropped out of grad school mere months before graduating and I’ve been moping around at home bouncing from one ineffective psych treatment to another.