Idk ball but maybe it's the result of the immense trauma he got from the abuse. He was abused by his own father, no one related to his problems, he was alone, scarred and the fear of loneliness in a doomed life led him to lash out on the little innocent brother who paints a different picture to him. He tries to inflict the pain he's been inflicted upon to atleast have someone who'll relate to him in some ways. I think there's some disturbing real psychology behind this and I can't be acting like yunoball here

I don't want to justify Sharif's actions, but he was also a victim of sexual abuse by his father. It’s a vicious cycle of abuse. He transitioned from victim to perpetrator. I truly want to grasp why he decided to inflict that same pain on his own innocent little brother... why?