Difficult situation...
I think, he bevahe ok, so I don't know why your mather throw all blame to him. I know, you did a really big mistake, but it's happend and you have nothing to do.
I think, maybe you can say your mother. But do it little by little, you know, say that you are still in contact with him... later say that you think his is really ok, and he try to help you to surviwe that sytuation... Maybe your Mother come to accept or like him
But give her some time, she have base to hate him...