Why does my ex's brother look at my Instagram stories?

He was somewhat involved in our breakup, since... they are best friends basically (my ex had friends, but not close friends)... I eliminated him and his wife from Facebook and unfollowed them on Instagram, but they still follow me. I didn't eliminate the rest of the family and I eliminated them because they're on my ex boyfriend's side and it hurt my feelings to know that blood IS thicker than water in that family (my family is not like that, they tell me how it is)...

Anyhow, my ex doesn't have social media, only his brother and SIL... his SIL doesn't always follow my stories, but my ex's brother ALWAYS does... why would he do that? I'm thinking about blocking them and unblocking right away just so that I don't have them being nosy... but at the same time, I like them to see what my ex is missing (everybody knew I was way out of his league)... I don't know...

Why does he look at each and every single one of my stories?