The speaker is writing directly to someone who has just hurt her badly. He has left her for another girl, one he was with before, who is pregnant by someone else. The poem opens with a rush of questions: why did you say that, did you ever care, was it all a lie? The short lines make it feel like she can't catch her breath.
Her feelings shift as she goes. There is confusion at first, then accusation. She reminds him of his promise not to run away and points out that he only thought about himself. Underneath the anger is a sadder note: "I thought you were different," followed by the bitter "Again," which suggests this isn't the first time she has been let down.
The ending turns inward. She admits how much she is hurting, but swears she will never let anyone see it. The repeated "NEVER" in capitals makes her vow sound fierce, though it also hints at how fragile she feels. The mood is raw, tense and defensive.