Loll no it is in chapter 13, it's the first page at the beginning. the chapter starts with his internal dialouge "since that day I did everything I could to avoid teacher" and "on Friday we had our shared class but he didnt try talking to me either. A week passed by just like that"
I think I explain it badly though he doesn't talk explicitly talk about his pheromones, I was trying to give background to op for why things are awkward between then right now. At the end of the last chapter (12) he can't control his pheromones to the point he has to excuse himself thinks to himself "I don't want to like him but I think i do"
Wait what happened between chp 12 and 13
Why Dohyun suddenly avoiding Wooyeon??