What should i do if my best friend is dating my boyfriends brother... i hate him and he is and ignorant jerk.?

my best friend shelby is dating my boyfriend's brother, John. They have been dating for a little. I have been dating Dustin over a year. I hate John for many reasons. He is a jerk to his brother and me. He is jealous because Dustin had a girlfriend before him. John tells me to stay out of other people' business but he goes and tells people that Dustin and I had . Even if we did it is NONE OF HIS BUSINESS. He is a total hypocrite. I CANNOT stand him. He has said so much rude stuff to her and me and she still goes out with him. I don't know what to do! I told her "John is a jerk and you shouldn't go out with him." And she will let him walk all over her. Even worse, they used my house as a meeting place and my house is not like a dating place. I hate him, I can't stand him AT ALL. He has a lot of girl's numbers in his phone. I wish he would do something so she would break up with him. If he wasn't a jerk I wouldn't care. I just need some advice here... fast PLEASE!