It looks like you’re referring to the Japanese adult visual novel / anime series (夫婦交換 ～戻れない夜～), often abbreviated with “th” possibly meaning “the” or a chapter number (e.g., “3rd” → “3th” → “th” typo). The title translates to “Couple Swap: The Night of No Return.”
Akane looked at Shinji. He looked away first. That’s when she knew — the marriage had already ended. They just hadn’t buried it yet.” **“They thought it was a game. Until they couldn’t stop playing. FUUFU KOUKAN – MODORENAI YORU No Return. No Regrets. No Innocence Left.” fuufu koukan modorenai yoru th
“‘Just one night,’ Ryo said, smiling. ‘No strings. No guilt. Just… honesty.’ It looks like you’re referring to the Japanese