He was afraid of what Kai could do once he tells him the reason why he was asking such a question. As known, there was no way Kai wouldn't want to know the reason why he was asking such a question.
He was doubting Kai would keep to the promise he made never to tell their father about what was happening to him at school once he tells him the reason why he was asking such a question.
Kai might be like, 'So after all this time that has passed, they're still bullying you at school? The main bullying stopped at some point, but it had resumed again?
I'm having a feeling these things happening to you at school would never stop, they might keep happening until it gets to your graduation. And I can't allow that, Ryan,
I'm sorry, I have to break the promise I made to you never to tell dad about what was happening to you at school. I'm doing this for your own good, I'm doing it to help you'.
