What does daisy tell gatsby that catches him off guard? what was he expecting to hear? how does nick describe the look on gatsby's face?

Daisy tells Gatsby that she loves both him and her husband

Gatsby was expecting to hear that she wanted only him

Nick sees that Gatsby has idealized Daisy, creating in his mind an illusion much more wonderful than Daisy actually is. He knows it's not Daisy's fault for not quite living up to Gatsby's expectations, because Gatsby's illusions are too grand and fantastic to be realistic.