Cesare never lied to Eileen. Rather than speak falsehoods, he prefers silence. He is always truthful with her, and this situation was no different. He meant every word he said. If Eileen promised him, he would reveal everything she wanted to know.
But Eileen couldn't make such a promise. The request shook her to the core.
Her mother had always taught her that their lives belonged to the Prince. Even her mother's final words had been for the Prince's sake.
"My dear Lily," her mother had whispered with parched lips, her face pale from illness.
"Live for the Prince."
Her mother's eyes had shone with a complex mix of jealousy, anger, and love, leaving an indelible mark on Eileen's heart—a curse of sorts.
Yet Eileen had willingly accepted that curse. Even without her mother's words, she would have lived for the Prince.
That's why she couldn't lie to Cesare by promising not to die for him.