Retarded is a synonym of mentally underdeveloped. If that's not the case, then it's just used incorrectly.
Usually because of social disdain for your behavior, and intended to degrade you into a lesser person than them.
Usually starts when your position on something irritates people who don't have any arguments other than your condition.
You've literally described how people around you make mistakes and put their weight on you. You are trying to reach them, but they are not trying to reach you. That's just wrong kind of people. I have friends and even neighbors not like this. Don't try to be good enough for some filth.
I don’t care what people call having multiple mental disabilities. What’s important is helping children on the spectrum. Early detection could have spared me further brain damage and subsequent stacking of developmental problems.
I care about both, but it's correct at least that people with such conditions should know about them as early as possible, to help with the challenges presented.
People shouldn’t think that starting a family with someone autistic is just “going to be a little different.”
Where I live people overthink that a lot. Somebody who had a few abusive relationships still thinks that one with an autistic person is worse because they are disabled or because they are crazy or some other ignorant caveman shit.
But you are right that for an autistic person a relationship with someone not conscious of all this is an idea that will fail without doubt. Because such people don't even know that one can think about relationships, it all works instinctively for them. They react to any diversion from the usual path the same way a Windows user reacts to a BSOD. They don't even see that nothing particularly bad has happened, are afraid to think and just run away.