Manazashi No Hayagane

From Girls’ Generation Scanlations:
Eri is careful to hide his true character. As luck would have it, one of the new teacher assistants under his care is Motou, an old student from his past. What will Eri do, faced with those candid eyes? Thus begins the tale – spanning over years – of a romance between a faithful teacher assistant and a masquerading teacher.
In the same cram school, love is budding between Motou’s hardworking friend, Izumi, and another awkward teacher named Makino. Their story is told in “Together”.