Douse Suterareru no nara, Saigo ni Suki ni Sasete Itadakimasu

Agnès, the daughter of a duke, is in love with crown prince Lucilleur, the man she's been betrothed to since they were both children. But before they can wed, Agnès is hit with a bombshell: Lucilleur doesn't return her feelings and wants to break their engagement so he can marry his true love, a different noblewoman with a sweet and innocent demeanor. Agnès is more than just heartbroken—she's angry. Her "sweet" rival might not be sweet at all, and her beloved prince has wrecked her future. This means war...both in politics and in bed.

(Source: Seven Seas Entertainment)