Nurse: Juliet's Ally, Then Her Betrayer

The Nurse is the play's comic centre in the first two acts. She is garrulous, warm, physically present in a way no other character is. Her long speech in Act 1, Scene 3 about Juliet's weaning goes on far longer than anyone needs, and is funnier for it. She clearly loves Juliet. She facilitates the relationship with Romeo with enthusiasm, carrying messages, covering for absences.

That makes her Act 3, Scene 5 advice hit harder. After Juliet's banishment of Romeo and her father's threat to disown her, the Nurse's counsel is pragmatic: marry Paris, Romeo is as good as dead to you, what difference does it make? It is survival logic, not treachery. But it is the wrong answer at exactly the wrong moment, and Juliet never forgives her.

'Thou and my bosom henceforth shall be twain,' Juliet says. A formal severing. From that point, Juliet is entirely alone with a plan no adult knows about.