Bichiku Oyako Chijoku Rankou Kareshi no Mae de Kegasarete by MorningStar - Adult Sex Game

Yuka Momose, an honors student seduced by a bad friend, gives her lover a birthday present and ends up having sex with him on the promise of showing him how she masturbates.
But right before his eyes, the gym teacher breaks a promise and shatters her virginity.
Yuka is photographed and forced into further physical liaisons. In the end, Yuki's mother, Kaoruko Momose, who is also a teacher, intervenes in the matter...