When Emily had said they should just throw caution to the wind and sleep together again.
He should have shot her down instantly. Telling her no in a firm voice.
Afterall, they had just barely managed to evade his uncle. It was too risky for them to be going back to sleeping with one another so soon.
Especially since she was suggesting that they take Monday as a treat instead of at least waiting for Thursday.
He should have disagreed with her. Told her that they could not do it. But the moment that Emily had told him that she wanted to go back to sleeping together. Derek had become powerless. She had taken the words right out of his fantasies after all.