She cared for none of her friends; she wanted no help of his; she would not hear of leaving Wickham; she was sure they should be married some time or other, and it did not much signify when. Since such were her feelings, it only remained, he thought, to secure and expedite a marriage, which, in his very first conversation with Wickham, he easily learnt had never been his design. He confessed himself obliged to leave the regiment on account of some debts of honour which were very pressing; and scrupled not to lay all the ill consequences of Lydia’s flight on her own folly alone.
– Jane Austen
Pride and Prejudice, Chapter 52. Mrs. Gardiner’s letter to Elizabeth tells how Darcy tracked down Lydia and Wickham in London and tried to persuade her to "quit her present disgraceful situation, and return to her friends." But he found Lydia absolutely resolved on remaining where she was. So Darcy determined to negotiate a marriage between the two, discovering that this had never been Wickham’s plan and he had left Brighton because of gambling debts there.