浮気された不遇令嬢ですが溺愛されて幸せになります

Alana, a duke's daughter, became the fiancée of Crown Prince Abel through a political marriage. She had been making blood-sweating efforts to become the future queen, but one day, she witnessed the unfaithful act between Abel and her biological younger sister, Avril. Despairing over the days she had spent and giving up on life, Alana asked her servant, Terence, to prepare poison and decided to end her life, but—!?