My heart goes out to you.
I have a gifted boy too and most of time will yell at us, screams and causes a riot to unfold at home (which eventually gets me and
DH to argue).
I believe that they really don't mean what they say. I believe it is a way for them to get their anger out because they are gifted/intelligent and their minds must work at a million times per minute. We don't understand what they are thinking, how they are thinking, what they are going through as we are not like them.
I really, honestly don't feel that he hates his mummy when your little boy says that. Just try and understand as to what he may be feeling and thinking when he says that he 'hates' you. I know it is hard to accept what he says, when you love him so dearly.
Do you have access to trained people in the area of autism which you could ask?
Goodluck xxoo