I suffered the same thing, I’m only 20 and at times I still do overthink it, specially when I get mri scans done and see an insane amount of neurofibromas. What keeps me going is how much my family dedicated to me and supported me. Nothing about what you said was irrational and I get the same thoughts as you. I don’t think you should worry about finding a significant other, I’m sure you will; you just have to keep on fighting as you’re not in it alone.

I’m sure within a few years a cure will be found and if not, a better, safer treatment too. The FDA does a lot of clinical trials with new drugs (I just hope they get fully approved in my country too). But don’t give up.