for anyone who's low-key confused, teacher basically cut his ties with yuri cuz he felt like it's not right for them to continue being together, Yuri started to catch feelings but jiri only see him as a former student, but knowing yuri seems to want something else from him, worries him. which is a big worry for a teacher like him. he draws a line before anything got big/worse (like the jiheon problem) cause he didn't want to drag yuri in it nor himself.