Kai couldn't help it. It wasn't like he hated his stepbrother who was disabled with autism slash asperger's syndrome. Kai was more like the take-it-easy type. His theory was, the things that people can't understand, can't hurt them. And Sehun, didn't understand most of the stuffs unless it was maths and technology.
He just didn't care much about his stepbrother. That's all. He was too busy with his own life to give special attentions to his stepbrother. His dad had remarried, when Kai was 13, to a woman with a son the same age as Kai after Kai's mother's death. Though Kai never felt a connection with his stepmother, he still respected her. Not as a mother but as a stepmother. During then, Kai knew his stepbrother wasn't normal. Sehun would never mingle around people. When they had visitors, he wouldn't even come out of his room. And not only that, Sehun also couldn't communicate properly with anyone. And that was one of the things Kai grew tired of that he stopped entertaining Sehun altogether.
At the age of 14, Kai's dad had sent him to an international boarding school in England. Ever since, Kai had never even talked to his stepbrother. Not even over the phone. It wasn't Kai's fault. Even when Kai unwillingly asked his dad to pass the phone to Sehun, Sehun wouldn't want to talk to him. His parents had flew back and forth to England to visit Kai at times but none of the times, Sehun ever came along.
So, yeah, Kai didn't hate Sehun. He just wasn't planning on getting close to him.