I'm going to call my sister's ex an asshole
Why would you call your sister's ex an asshole
This guy is a disrespectful son of a bitch.
This person is not involved with your sister anymore so you need to move on from the situation and stay out of it. Don't you think you might cause more problems if you get involved again?
I'm not going to turn the other cheek, he's a prick for leaving my sister for another woman.
If he is willing to cheat on her maybe it is best she is out of that relationship. I think she got away from a potentially worse relationship.