my sister the traitor

So I was on Instagram right, and they have this thing where they recommend you to follow someone because you have a mutual friend that follows that person. I found out that my sister follows my "ex-boyfriend" (quotes because it was kind of this on-again-off-again thing, and I don't really consider him my boyfriend because it lasted like a week both times) on Instagram.  And he follows her.  I was really upset because I've vocally expressed my disgust for the guy, and I feel that as my sister you should hate someone that I hate. And she was like what's he ever done to you, he's actually really nice.  Like excuse me, I don't remember you being the one who had a "relationship" with him. Twice!   And I didn't tell her that he's gross because he's sex crazed and tried to make me fuck him in a bathroom at a park but I was like no.  Because that's kind of an embarrassing thing to admit since I put myself in that position in the first place.  Also, he tried to steal my first kiss from me but idk if he did it right so I don't count it.b anyway, the point is the least she could do is unfollow my enemy, right?