Schoolboy Crush (2007)

Kairo Aoi, a young teacher with striking good looks, has just learned that his new student, Sora Amakami, is the alluring teen prostitute he once hired. Here the nightmare begins. As the walls of the prestigious academy become a percolating hotbed of sexual intrigue, prostitution and blackmail, other students, including Sora's nerdy roommate and the sinister campus bully, are pulled down the same torrid path of unquenchable desire toward the inevitable moment when obsession turns deadly.

Source: TMDb