Sundome 3

The high school boy and girl from "Sundome 2" continue their sexless relationship in which she is sadistic and he is masochistic, but one day there is a rumour at school about her having a relationship with a different—and older—man. The boyfriend feels as if his girlfriend is hiding her relationship with the older man.
(Source: Letterboxd)
~~ Adapted from the manga series "Sundome" (すんドめ) by Okada Kazuto (岡田和人).