Help plz

I need help finding a black and white manga. It was about a girl in high school and the ml was a teacher?nurse?counselor? Idk and he was friends with the fls brother(the brother didn’t show up much)and i don’t remember seeing the family. She was a tsundere type, and he flirted with her but never actually pursued her idk his character was complicated. They both have black hair, there was also a blond hair kid that liked fl and thought the relationship between fl and ml was weird. I think fl also was a loner and had a certain mindset that made the ml want to give her motivation? I don’t remember I think fl lived alone too. I think there was a train track scene too
Yeah…that’s all I can remember