LOLA

my BF sister has wrecked my friendship with BF.
The sister treats me like sh t, has no problem yelling and name calling, emotional manipulative (which the BF hasnt seen this side of her). The problem is there is no way I would have put up with any of this expect that I dont want lose my BF. But it has come to a point where Im over it and have to make a stand for myself, otherwise Im saying its ok to treat me like this. BF knows there is a problem, but doesnt want to go into details, which is fair enough, but it feels like the sister has posended her against me, and I cant say well actually this is what happened. Other people have witness it and are in shock at what the sister has actually done, so I know Im not over reacting. And the problem with it is I have tried to approach it with the sister in a non aggressive way using I statements rather than you statements but its fallen on deaf ears. The problem is I find the sister to be quiet evil and there is NO way I would be talking to her at all if I wasnt friends with her sister.....plse help