"You can't tell me I don't know who you are," Meredith says, "and then leave it there. You can't do that. Start at the beginning. Jump into the middle. Just start somewhere." It's not like she thinks he's lying now. Whatever's got him like this, he means it, she's sure enough of that. This isn't the kind of thing someone does in the middle of the night just for kicks. She just doesn't believe him, that's all. Maybe it's as much stubbornness and pride as sheer, unwavering faith, but whatever the reason, she loves him enough to think he's utterly, stupidly wrong.