Prince Charming (2004)

Blurb:
Asahina-sensei isn’t a very good teacher or a role model. The epitome of a letch, he spends his nights cruising the town, hooking up with one woman after another—he’s even been known to stumble into class drunk—but Asahina’s sordid lifestyle has finally caught up with him. When Yuasa, one of his students, finds a video of Asahina having sex in a love hotel, the proof of his degenerate behavior is clear. Yuasa promises to hunt down the master tape and keep Asahina’s secret—for a price, of course. With love as Yuasa’s payment of choice, will Asahina be able to meet the asking price?

Source: www.anisearch.com/manga/2015