Responses
I think it's more like the teacher thought that the the school doctor was always held by guys, all the time, and he didn't care having another one man on his plate. Thus sleeping around with men was his hobby or some sort of thing ¯_(ツ)_/¯
I think you need to reread the dialogue carefully
"Oh ! You're thirty-something and you already had sex ?! You're a total bitch !" Ahhh... Japan through manga ┑(￣Д ￣)┍.