Koi no Jumon

After dumped by yet another girlfriend, Mihara, a teacher at a prep school who is trying to get a job teaching at his old high school, goes to a gay bar to try and prove that he’s not gay. There, he is noticed by Shouta, an openly gay high school student, who takes him away from the gay bar and, well, makes his move. This bothers Mihara, who is adamant about the fact that he will never like a guy, and remembers a time when he said exactly that to a friend. But the next day, Shouta shows up at his prep school (which is for elementary school kids ^_^), and he finds out that Shouta is a student at his old high school! And in fact, Shouta claims to have fallen for Mihara and refuses to leave him alone, no matter how much Mihara refuses him. But it seems that there is more to Shouta, and his past, than his perky behavior seems to suggest… and Mihara just can’t stop himself from getting drawn to him. Even so, Mihara continues to find himself bound by the "curse" of the words he used to turn down his friend way back when…

(Source: The Lemming's Obsession)