Unless her sadistic actions endanger your safety or the safety of your family try your best to simply tolerate her. The easiest solution is to ignore her and avoid putting your boyfriend in the middle. But if you absolutely can't tolerate her, talk to your boyfriend and hear what he has to say. If he doesn't want to get involved at least he'll understand why you're feeling so uncomfortable around her. And if you still can't handle his family seriously think about your future with your boyfriend.
Family is forever, but marriages come and go.
I can't understand what went wrong. I have always tried to leave the lines of communication open. And I told him when the relationship initially started not to hurt me. I've never opened my heart to anyone. I've never loved anyone.