Teach should just ask Guwon if he actually killed his dad and also that he still feels uncomfortable and sad because of the murdering of the doctor. In that sense teach should open up more and have a talk with Guwon. He's obviously not going to tell him about the rebellion. But clear the air with the whole dad topic. This is the main reason why their dynamic changed so much and the vibe went sour

This reminds me of From. A lot of issues could be resolved with some open and honest communication.