A speaker lies awake beside a sleeping partner and hears them murmuring a name that isn't hers. That small moment sets off a spiral of suspicion. The poem is built almost entirely from questions: Is it just a dream? Is it imagination? Is it a memory of an old affair? Each one tries to calm the worry, yet each one only opens the door to another.
The speaker's feelings are tangled. There is jealousy, but also real confusion, since she admits she has never had a reason to mistrust this person before. That line shows how much the discovery has shaken her. The detail that the dream seems "sensual" makes the hurt sharper, because it suggests intimacy she can't see or share.
The mood is quiet, uneasy, and vulnerable. The short, plain lines feel like private thoughts in the middle of the night, and the final question, "And how can I know?", leaves her with no answer and the reader with the same uncertainty.