With his sister in serious trouble, he may have to sacrifice this and offer an explosive photo to the tabloids--the same tabloids that ruined Daisy's mother's life with stories fed to them by his father (and Daisy's mother's ex-wife). He certainly can't tell Daisy he needs protection against a man trying to prevent Nick from doing exactly the same type of damage to his reputation. Still, he knows exactly what lying to Daisy will mean. He certainly hasn't forgotten that one night years before and still wonders if he might have made a mistake.