"Ruin me," Della said sternly. "I want you to ruin me. I want you." If she had to die for this, so be it. She was so desperate to get away from this hell-like life that she had been living for years. Not to mention the tradition, where the men could get whatever they wanted without any consequences. But when the women did the same, only dire fate awaited them.
Della wanted to do what Aeon did to her. It was a slap to his face whenever she was with Aderan, because the King thought he had her under his thumb.
She wanted to do it with multiple people, which would give her delight because it would humiliate Aeon, but then she couldn't bring herself to do so since she had Aderan. The thought of betraying him was way more terrifying than the thought of betraying the King.