Tsuma no JK Imouto to no Gakunai Inkou ~Yamerarenai, Haitoku e no Yuuwaku~ by Appetite - Adult Sex Game

Bed in the infirmary. Behind closed curtains.
"Hey honey, are you okay?"
"I'm fine, I'm fine. I'm fine."
Taadki's answer to his wife Sachiko.
The protagonist Tadaaki is talking to a nurse behind a curtain.
Chica, his wife's sister, knelt down and used her mouth and breasts to suck him off.
"No. I have to make her stop before my wife hears!
"You must stop now."
Tadaaki whispered to her so that his wife would not hear. But Chika didn't stop.
"I want you to feel good. Am I doing everything right?"
"Because you are mine..."
After that, Chika never tried to stop "serving" Tadaaki. And he, in turn, wanted it more and more.
Behind the curtain is his wife.
Under such circumstances, Tadaaki could not refuse Chika, he was too infatuated with her.