I hate my sisters girlfriend?

Ok my twin sister is a butch (that means please dont say anything,i still love her). Her girlfriend is a hoe (thats in nice terms). We are 13 but her girlfriend is 14. Her girlfriend is bi and most times I wonder if she is just using my sister because a guy will ask her out, she will break up with my sister and then her boyfriend breaks up with her because she cheated on him and then she comes back to my sister because my sister will take her back because shes liked her for 2 years.Its a process that has happened like 4 or 5 times.She was talking the other day about her boyfriend (shes supposed to be dating my sister at this time) she said she has liked this guy for 3 years and he doesnt care that she is also going out with my sister,but she even said that my sister doesnt know and if she did she would be mad.One day she told me she was jelous of because she thought my boyfriend was hot but she also tells me how funny my sister is and how she likes her.I want to try and talk to my sister but im scared she might get mad.I know she would be heart broken because she has liked her a long time,and thats why she keeps taking her back.Apart of me feels like i should tell her but the other part of me feels like I should mind my own buisness.Should I tell my sister?