Tom deferred that much to the sensibilities of those East Eggers who might be on the train.
This describes the practice of Tom’s mistress sitting discreetly in another car while they take the train together into New York, despite their frequenting of popular restaurants in the city, where he would leave her at the table and saunter about chatting with whomsoever he knew.
Once I took the train from West to East Berlin, not long after the Berlin Wall fell with the end of Soviet Communism. Getting on the train in West Berlin, I noticed a young couple, a bland German youth and his girlfriend, a dark Arabic girl. They stood with arms about each other as the journey started, frequently leaning in to exercise their new love in a kiss, but their public affection became more and more subtle as we headed East. Finally, by the time we crossed over into the formerly Communist, and still very conservative, part of the city, they stood at opposite ends of the train car, connected only by their longing glances into each others eyes.
Terribly romantic and quite unlike Tom and Myrtle, but that’s what I think of each time I read this passage; the burden of deferring passion for the sensibilities of others.