Without a doubt, Tsutsugou is gonna know Sensei was there; whether its his shoes, his scent(prob this), or whatever. Then she'll get her turn to have Sensei.
I guess it was inevitable he'd start to feel something. Not just because 'manga plot', but I'm sure it was easy to disassociate from these girls because he felt like he led a different life than they did. Now that he's seen the more vulnerable side to them, it makes them more relatable. They're more than "just students"; but people who endured similar psychological issues, and those emotions will ultimately come into play even against his immovable logic and morality.