Why do people assume you'll be lonely and miserable if you abstain from sex and relationships?

Humans are wired to be social creatures and love is part of that.

I don't believe that you aren't smart enough to figure out by yourself that people draw tendencies from general (averaged) behavior.

If you go to a school and look at the distribution of grades and it happens that they're mostly C's, then you should expect that a student picked at random will be an average student. You shouldn't expect to pick one by random who's either a straight A's student or a quite mediocre one. That's what "average expectation" is about.

Stop being so worried about what others think. They're just reflecting an expectation from typically observed behavior. Just like when women assume that a guy is up to no good if he happens to be walking behind her at night on the street; it doesn't mean that he's out to harm her, but that's what women assume. That's just what people do.

it is. Goon on you sir or madame.