Kataomoi ga Tsurakute Shissoshitara, Yandere-kashita Otto ni Tsukamarimashita

"I've been searching for you for the past year, even sacrificing sleep." Former fourth princess Carol is deeply in love with her husband, Alan, a marquis and the commander of the kingdom's knights. However, this marriage was arranged by her father, the king, upon her request. After three years in a white marriage, she learns that Alan had actually been in love with her older sister, the first princess, all along, so she decides to set him free and disappears, only leaving behind divorce papers. A year passes, and just when Carol thought those two would probably be happy by now, Alan suddenly appears, seemingly changed...?! https://www.cmoa.jp/title/346197/