At first, Juliet wants Romeo to stay and is trying to convince him it's still the middle of the night. She tells him it is a night bird that he is hearing, not one that makes noise near to sunrise. She tells him it's a meteor he is seeing that is making the light, not the sun.
But then Romeo says he doesn't want to go -- he says it's fine if they catch him and kill him, he doesn't care. So then Juliet decides he'd better go so that he can live to see another day.
She says he looks pale as if he's in a tomb -- it's foreshadowing how he'll look the next time she sees him.
