Responses
Is it hironaka no ryuusei?
Actually I think you might be talking about http://www.mangago.me/read-manga/ao_haru_ride/
I don't think so. Kou was in love with futaba and it's kinda more like futaba's friend is in love with the teacher rather than the opposite.
About hirunaka no ryuusei, didn't the girl was in love with teacher and then she decided to be with a male student rather than the teacher.
I haven't finished the manga yet so I might be wrong ╮(￣▽￣)╭
About a year ago i read a shoujo manga (only had one chapter out at the time, i believe) about a male teacher who was in love with a felmale student and a male student in love with a female teacher(?) (Either teacher or school nurse, i don't remember) i've been searching for it but can't find it :(