The sex isn't as good as it ought to be, and Emma knows that this is because she isn't who the one Erik wants. Not really, though he's decided to settle for her for now.
He's a convincing faker, but she's not easy to fool, not when she can hear the name his mind groans out when they're in bed together. He says that it doesn't matter, that he wants her, but she knows when someone is lying to himself.
She has a sense of using, or of being used. She's not sure which.
Either way, she's used to it.