Douse Suterareru no nara, Saigo ni Suki ni Sasete Itadakimasu

Agnes, the daughter of a marquise, is told that her long-time unrequited love and fiancé, the crown-prince Lucilleur, has called off their engagement, while standing next to another woman. If he will never love her anyway, if he will only abandon and oppress her, then she will finally... be free. Agnes had done so much defend her home, her freedom, and her pride, which made her become obsessed with Lucilleur. Two stubborn people who are unable to be honest with each other, and the course of their entangled love story will lead to... (Source: Ichijinsha, translated)