I'm Secretly Fucking My Girlfriend's Mom Behind Her Back — Mary Tachibana

Original title: 彼女に内緒で彼女の母ともヤってます… 橘メアリー

“Behind her back and in her home: Drowning in a forbidden affair with my girlfriend's mom”

The protagonist has started a high-risk secret affair with his girlfriend's mother, the seductive Mary Tachibana. While the daughter is away, they indulge in their forbidden desires, risking everything for the thrill of the betrayal.