Ai mo Dokusenyoku mo Hageshii Kishi Dannasama no XL wo Uketomekiremasen! Itsuwari Dokufu wa Maiyo Midara ni Dakitsukusareru

Lady Federica is rumored to be a femme fatale because of her voluptuous and alluring appearance. In truth, she is a pure and innocent maiden, but the gossip has left her on the verge of becoming an old maid. Just when she has nearly given up on marriage, her childhood friend Rinaldo, a knight, proposes to her. Rinaldo explains that he has caught the eye of a princess and is troubled by it, and that marrying Federica would benefit them both. Seeing it as an unexpectedly favorable arrangement, Federica steels herself for a marriage of convenience—only to discover that it will not be a sham at all, but a true husband-and-wife relationship that includes sharing a bed. With his powerful hips, heated gaze, and large body that presses the breath out of her, Rinaldo—a man with monstrous stamina—demands her fiercely every night.

(Source: Overlap, translated)