She was more understanding than he'd given her credit for. That was a relief in more ways than one, and Lelouch allowed himself to relax a little. He had no doubt that they would never see eye to eye on certain topics, but at least she seemed willing to accommodate for a few of his lesser sins. Lying in the ways he'd mentioned didn't even strike him as especially harmful (how could it?), but if she took issue with it-- it was so much harder to do things she disapproved of when she knew he was doing them. It was even harder when, as in this case, his reasons for doing so were becoming flimsier with every curve the institute threw at him. Hiding the things he'd done as Emperor was obvious enough, as was concealing the full extent of his Geass's power and so forth, but the fact that he was a prince and Zero... would revealing those at this stage really harm more than help? Would it have any effect at all?

"You need only ask," he said, looking up at her again. "I won't lie to or hide things from you anymore, Nunnally. You have my word." As he had with Suzaku, he knew he was treading dangerous ground by making such a promise, but again, he was tired of lying. He should never have lied to Nunnally in the first place, and although he was, in his mind, far guiltier of hiding things from her rather than lying outright, it didn't matter anymore. She had a right to know what he was keeping from her, and with the Lelouch she had known gone, the task of explaining it all fell to him.