Bakunyuu Jukujo na Bitch Kanrinin-san to Tsukiau Koto ni Natta Kekka wwwwww

Kouhei (protag) who lived in a student boarding house hooked up with the housemother, Kyoko.
She disposed of his virginity and never left him wanting.
Kouhei was happy, but one day a gut-wrenching incident stared him in the face.
He saw her, his lover, his girlfriend Kyoko, having sex with another boarder.
He flipped out and dug for the truth.
That truth that Kyoko was a massive nymphomaniac beyond anything he imagined.
What's a guy to do? Kouhei!!

[From DLSite English]