He'd suspected that she was Christine, but hadn't known - not until after the moon. Denial had only managed to last that long. "She didn't tell me anything about you. I didn't know you were Christine, not until after... in the catacombs." Taking her down there had been Erik, not him; he did like the seclusion, but he wasn't deluded enough to think that he could keep her down there. He didn't want to, because it wasn't the same.
Bran was speechless for a few moments, trying to wrap his head around the fact that she'd trusted him and in a few minutes he'd ruined that. "Why did I let you go?" He echoed her question, confused. "Erik took Christine down there, because he was confused and didn't realize what was going on. I didn't want to keep you locked up down there." What he did want in terms of Lotte was still hazy, and after helping her get her confidence back there really wasn't a set plan. Once she was singing, he supposed that would be enough... or was singing for him what he needed?
"I don't know. It probably shouldn't." Why did it matter? It probably had something to do with how miserable he would have been if something had ruined music for him like the voices had ruined singing for her.