“Tom’s got some woman in New York.”
Jordan is aware of Tom’s mistress that he frequently went to visit — evidently it wasn’t a secret in the West Egg.
Notice the way Jordan describes the girl, too. She just calls her “some woman” which hints that this might not be the first time Tom has found a mistress.
To help improve the meaning of these lyrics, visit "The Great Gatsby (Chapter I)" by F. Scott Fitzgerald and leave a comment on the lyrics box