The motive professed was his conviction of its being owing to himself that Wickham’s worthlessness had not been so well known as to make it impossible for any young woman of character to love or confide in him. He generously imputed the whole to his mistaken pride, and confessed that he had before thought it beneath him to lay his private actions open to the world. His character was to speak for itself. He called it, therefore, his duty to step forward, and endeavour to remedy an evil which had been brought on by himself. If he had another motive, I am sure it would never disgrace him.
– Jane Austen
Pride and Prejudice, Chapter 52. Mrs. Gardiner writes a long letter to Elizabeth detailing how Darcy effectively negotiated and paid for the marriage of Wickham and Lydia. He traveled to London and found them, persuaded Wickham to marry Lydia by paying him a substantial sum of money and arranging a commission in the army, and got Mr. Gardiner to take credit for everything. Mrs. Gardiner’s letter speaks about Darcy’s professed motive for saving Lydia, but also hints at another motive – his love for Elizabeth.