“And what about little thing? Leo? He wasn’t beautiful exactly, I wouldn’t have thought. You were crazy about him.” She looked at him interestedly to see if she’d gone too far. Nick said solemnly but feebly, “Well, he was beautiful to me.” “Exactly!” said Catherine. “People are lovely because we love them, not the other way round.” “Hmm.”
This is the passage everyone highlights, but it's really the next one that represents Nick's actual views on the matter.