Thanks.

I can see from my sister's perspective why she thinks it's "okay" to be b_tchy, and why there's no reason for her to be respectful toward others. I mean, she literally gets away with it every single time, so what reason does she have to change?

In my opinion, her boyfriend should breakup with her for his own sanity, but I think he's too chicken to do that. She abuses the hell out of him: She yells at him and whines, and she commands him to do things... and yet, he puts up with it. He shouldn't. But it's not my place to tell him to break up with her. I just hope he realizes that she's not going to change, and that if they get married, he will have to deal with the abuse and manipulation for the rest of his life.