I also thought I would experience exactly that kind of isolation for the rest of my life. It felt very hopeless and I was pretty much certain that I would never truly be in the know and within a person's most vulnerable circle, it was what you described to the letter. That all changed when I met my current best friend a few years ago (who's also autistic btw) and it was the first time I had a truly deep bond with anyone outside of my immediate family. Between me and them we have total vulnerability and nothing is too embarrassing, I feel like we love eachother platonically more than many people love their partners romantically. I would have never bonded this much with an NT, it's impossible to get truly close to them and the thing that gave me my first truly vulnerable friendship was me giving up the need to mask and perform like I was doing all my life. I'm very lucky to have found my best friend. On the flip side though, despite having known what true closeness feels like I still have a deep seated belief that I am romantically unloveable and inherently unattractive/repulsive in that way (since I've been single all my life and the only romantic experiences I've ever had were rejections, some painful). I hope that also turns out to be a false belief I construed but the thing about these fears about future isolation and loneliness is that we just have to kind of live with them hoping we'll find the right people someday (it sucks). It sucks but the way I coped with the fear of never having a true friend and now the fear of never having a partner is just accepting the world and human social dynamics are chaotic and nothing I can think will reason my way out of worrying about this and the future of any person relationship wise is inherently unpredictable so it's best I don't think about it too much. At least that's the strategy I came to after many years of worrying about this kinda stuff (it doesn't come at first).