One night and two days of 1 night and left alone by my wife's sister who suddenly came over

Yuji was enjoying living alone for the first time in a while. My wife is back from home because she's pregnant. Then, her sister-in-law Miyuki came to check on Yuji, who was alone, worried about him. Yuji, who was fed up with the rough house, invited him to the house, saying that he was lucky enough to do so... Miyuki suddenly started to say something strange with a suspicious smile. "The most common rate of men cheating is when their wife is pregnant. Isn't Yuuji having accumulated too?" She said, staring at Yuuji as if she was aiming for prey...