Read With a strong-willed Marchioness, Prince Yandere's Love Offensive Manga:
Agnès has been engaged in an arranged, political engagement with Lucile since childhood and fell in love with him upon meeting him. Lucile however does not return these feelings and sees the marriage as purely political. Now adults, Lucile wishes to break off engagements and marry the one he truly loves, Agnès however will not go down so easily.