Could this be It Seems Like I Got Reincarnated Into The World of a Yandere Otome Game...?
Déjà vu—Licorice Radiata knows it all too well. Throughout her entire life, she has been plagued by vague feelings that everything has previously already come to pass. Then, after seeing a portrait of her fiancé Wolfgang Eisenhut, a surge of memories flow into her head: she is the rival character of a yandere otome game, and Wolfgang is one of the many "target" characters.
In the original storyline, Licorice was the jealous rival, committing terrible and violent acts, and even in the heroine's good ending, she would die a bloody death. Mustering her courage and scattered recollections, Licorice is ready to do whatever it takes to avoid such a dreadful downfall, but can she prevent Wolfgang from becoming a yandere? It is not that simple to alter the course of fate, and she may have to accept that one's nature is not so easily changed.
The protagonist is Lycoris Radiata, the brown-haired daughter of a duke. When she's ten years old, her father shows her a portrait of Wolfgang Eisenhut, the black-haired son of another duke.
The moment Lycoris sees the image of Wolfgang's face, her mind is flooded with memories from a previous life. She was realises that she was an officer worker in another world, who was killed in a traffic accident, and that she's been reincarnated into the world of an otome game she used to play. Her character, Lycoris, is due to become the rival of the heroine, and Wolfgang is due to become her fiancée, and then possibly kill her in one of the game's routes.
Their fathers want them to become engaged to one another, and eventually produce heirs for both families, and so Lycoris and Wolfgang are formally introduced, in person. As soon as they're left alone together though, Wolfgang makes it clear to Lycoris that he isn't attracted to her, and that he doesn't want her to "misunderstand" her position as his fiancée.
Lycoris suggests that they both agree to the engagement for the time being, so their fathers won't keep bringing the subject up, but then later break it off when Wolfgang meets a girl he actually wants to marry. As the story progresses though, they both develop stronger feelings for one another, and both later attend the same magic academy.