"The expression of his face changed gradually from indignant contempt to a composed and steady gravity."

I fear Darcy's thoughts at this moment are turning him away from Elizabeth rather than closer to her. He's been fighting his attraction to her by reminding himself of her low connections, and her mother's comments are the strongest proof he needs that any alliance with the Bennets would be intolerable. He's also just learned that common gossip says his best friend is about to marry into the family and judging from the "very serious" look he gave Bingley and Jane, he doesn't approve.