"I know", he interrupts, knowing exactly what she meant having visited her memory of that night multiple times in their pensieve. That first time he visited that particular memory, he was in awe, it was their first date yet part of her was picturing a future with him, a future that involved their children. He was already in love with her at this point, but he feels that this was the start of it for her and will always be one of the most precious memories for him.