My Beloved Stepbrother: The Possessive Love of the Sadistic Marquis

Alice and Gilbert became siblings when their parents remarried. Alice fell in love with her stepbrother the moment they met. Since then, she has been nurturing these feelings, knowing that it is forbidden for a brother and sister. One day, Alice hears a rumor that Gilbert, now a duke, might marry a princess, and she becomes deeply troubled. Deciding that she would rather have him than let him be taken by another woman, she tries to give Gilbert an aphrodisiac to initiate a relationship. But she accidentally consumes it herself! Source: BisouBisou Comics