I don't mean to pry, but I'm kinda curious. What do you mean by function well in society? Some people with down syndrome can still live a semi-normal life and be employed, are you saying your son is worse than that? Can he talk to people? Can he drive?
Race is a social construct in the same way that dog breeds are a social construct. They're fuzzy and often overlap, but they do correspond to some underlying biological reality. They're not an artificial political creation.
What do you mean by seriously autistic? You said in another post he does tasks around the house and took care of your wife when she fell ill. A seriously autistic person would not be able to do that. A seriously autistic person would require constant adult supervision.
Are you sure he's not just under-socialized and addicted to porn and video games? How does he spend his days? He might simply be a western hikikomori.
I'm not sure how old you are, but among young men there is a big problem with sexlessness. I think I remember reading recently in the newspapers that 1/3rd of young men are incels nowadays.
Well of course, a woman's sexual value plummets after her mid 30s (also known as "hitting the wall"). However, 25 is still young and a 25 year old girl has an almost unlimited amount of options if she tries online dating.