‘Who wants to go to town?’ demanded Daisy insistently. Gatsby’s eyes floated toward her. ‘Ah,’ she cried, ‘you look so cool.’
Their eyes met, and they stared together at each other, alone in space. With an effort she glanced down at the table.
‘You always look so cool,’ she repeated.
She had told him that she loved him, and Tom Buchanan saw. He was astounded. His mouth opened a little, and he looked at Gatsby, and then back at Daisy as if he had just recognized her as some one he knew a long time ago.

F. Scott Fitzgerald

The Great Gatsby. Chapter 7, Daisy’s confession of love for Gatsby. Though they don’t speak of love aloud, it is clear to Daisy’s husband Tom from their behavior that Daisy and Gatsby are having an affair – much like Tom is.