Author is still kind of jerking us around. MC acts dumbfounded like he had no fucking idea. I'm always surprised by this sort of stuff, like, first off, he's a man. If he's a normal guy he's at least considered his feelings toward every attractive young woman that he's been in close proximity to. The idea that he's just suddenly blindsided is silly. No one's THAT dense, and if he WERE that dense, he'd just immediately reject all of them. You don't fall for someone because they fell for you, there has to be an initial attraction on both ends to begin with.
Anyways, not sure exactly what the proper procedure would be in Japan, but I've worked in American schools and if a student said something like this to a school employee, that employee must immediately go to the principal and report that inappropriate statement, and the student would find him or herself in the counselor's office within the day to get a firm lesson on why it's inappropriate to say things like that, etc., and the teacher would make sure he or she is never alone for even a split second with that student again.
In fact that's the standard policy for many teachers - especially male ones -- to never, ever, ever, ever, EVER be in a closed room or anywhere else, one-on-one with a student, because even the smallest whiff of an allegation or improper relationship could permanently tank their careers.