Remember back at Netherfield when Elizabeth and Darcy discussed Bingley's pliability? Elizabeth seemed to think it the mark of a good friend, while Darcy did not approve.

"To yield readily -- easily -- to the persuasion of a friend is no merit with you."
"To yield without conviction is no compliment to the understanding of either."
"You appear to me, Mr. Darcy, to allow nothing for the influence of friendship and affection. A regard for the requester would often make one readily yield to a request without waiting for arguments to reason one into it. I am not particularly speaking of such a case as you have supposed about Mr. Bingley. We may as well wait, perhaps, till the circumstance occurs before we discuss the discretion of his behaviour thereupon. (Ch. 10)

Well, now the circumstance has occurred and Elizabeth has changed her tune.

…and much as she had always been disposed to like him, she could not think without anger, hardly without contempt, on that easiness of temper, that want of proper resolution, which now made him the slave of his designing friends, and led him to sacrifice his own happiness to the caprice of their inclinations.(Ch. 24)