Netsujou

From DMP:
Hikaru, a second year high school student, is obsessed with Shima, a male teacher. Surprisingly, Shima is not averse to the boy's affections. He even convinces Hikaru to study hard and they will be "pretend lovers" for Hikaru's last year in high school. However, Amamiya, another teacher at the school and an ex-lover of Shima, steps into the picture and tries to win him back.
Will Hikaru and Shima's passion prove great enough to hurdle all the obstacles stacked against them?