For My Adorable Fiance's Sake summary:
The world, it seems like it is that of the Otome game "Welcome Princess", but there's something off!? Elliot, the eldest son of a Marquis family and one of the targets you can go after is an insanely handsome young man, both cool and wicked, master of both pen and sword. His only weakness (?) is that he is "hopelessly in love with his (the villainess?) fiance Francine!" The story of Elliot and how he began drowning in love for his fiance at the age of 7 starts here.