“What do you want money for, all of a sudden?”
Tom can’t believe that Myrtle would consent to leaving town and not being with Tom anymore. So he implies that Mr. Wilson is the only one who actually wants to leave.
Tom’s wife is already driving away with the man she is cheating on him with (Gatsby), and now the news that his mistress will also be leaving town is overwhelming him.
To help improve the meaning of these lyrics, visit "The Great Gatsby (Chapter VII)" by F. Scott Fitzgerald and leave a comment on the lyrics box