Imouto ni Konyakusha wo Toraretara Mishiranu Koushaku-sama ni Kyuukonsaremashita

When she breaks off a bad engagement, the young duke proposes marriage to her and she goes into love mode! Amalia, a countess whose sister has stolen her fiancé, becomes desperate and goes to a nightclub. There, she gets drunk and tells a young man who is talking to her about her situation. The drink overwhelms her and Amalia asks him to help her break the engagement, but discovers that he is actually the young duke... A beautiful love story about an unhappy young woman whose fiancé has been stolen from her, and whose life is turned upside down when she is treated with affection by a Yandere duke. Source: MU