Kaibutsuhime no Kyuuai

Sereniel was once a beautiful princess beloved by her people, until she was struck by a curse that disfigured her face, which led to her becoming known as the “Monster Princess.” Her parents shunned her and isolated her from the public, and the only person who treated her kindly was the knight Cassel. Sereniel had given up on her love for Cassel because of the curse. But one night at a party, she runs into Cassel, who has been drugged with an aphrodisiac, and they end up spending the night together. Forced by marry by royal decree, Sereniel is haunted by a strong sense of guilt that she had deprived Cassel of a happy future. Sereniel wants to free Cassel, so she asks him for a divorce. However, she received an unexpected answer. "I have no intention of letting you go." Sereniel believes that she will never be loved, and Cassel does not want to lose her. What will happen to their painful love affair? (Source: Comico, translated)