Sensei wa Ore no Mono

Third-year high school student Tachibana Kyou's world is shaken when a green-horn nurse suddenly arrives at his exclusively male school—the doe-eyed, baby-faced, and irresistably adorable Hirota Natsu. Completely taken with the new faculty member, Kyou abandons his playboy lifestyle for her, having found true love for the first time... But what will fate have in store for these two, engaged in the taboo relationship between teacher and pupil...!?

(Source: CoyoMoose)

Sensei wa Ore no Mono is based on a cell-phone novel of the same title.