As far as I know, prepositions are followed by a noun or noun phrase or a wh-clause. But the following sentence confused me because the author used a complete sentence after the "for".
But evidently the sound of it pleased Gastby for Tom remained "the polo player" for the rest of the evening.
I don't understand why the author didn't use this form :
But evidently the sound of it pleased Gastby for Tom remaining "the polo player" for the rest of the evening