I hate my boyfriends brothers girlfriend. HELP

Okay I really need some help here lol. So me and my boyfriend have been dating for 3 years. We're very serious and love each other. My boyfriend has a brother, who is 2 years older and has a gf(also 2 years older) that hes has been dating for about 4 years. His gf and me used to be friendly and say hi to each other and we were fine, but one day out of the blue she just stopped saying hi to me every time I saw her at my bfs house and wouldn't even make eye contact with me. It was SO RANDOM. Then she unfollowed me on all Social media, then she started giving me dirty looks and would talk trash about me to people that I knew who told me. I ignored it and just ignored her. I told my boyfriend about it and he wasn't happy but he's still nice to her and it really gets me angry. One day my bf asked her why she's so rude to me and she said that she's not and she has no problem with me(LIE). She is such a BITCH!!!!!! Now I don't even talk to her but heres the worst part... My bf still is decently nice to her but tells me he hates her(WTF) ...she acts so innocent and tries to put on this act. She's clearly trying to get my bf to like her and make me mad.. It's totally working. I just don't understand how my bf could be nice to her when this girl trash talks me and gives me shit looks all the time. She also talks shit about my bfs family right infront of him and his brother and it gets me so pissed because they're like my family too!! Anyway, this has been going on about 2 years and I Just need to ignore her and move on I just don't know how to. I hate her so much it's just too much work to keep hating this girl. I have TRIED to be friend with her but she is just a stubborn bitch. I need to find a way to just ignore the situation....