What is the main conflict in The Garden of Eden by Ernest Hemingway?

David and Catherine Bourne are on an extended European honeymoon, traveling freely long the Mediterranean coast of France and into Spain. The idyllic vacation is interrupted first by Catherine's sexual role-playing. David cooperates, although it makes him uncomfortable. When Catherine picks up a girl in Cannes, she makes it clear that she expects both of them to make love to the new girl. At Catherine's instigation, David has sex with Marita, although it makes him feel disloyal. Soon, Catherine has designated women as a "wife of the day," and David is alternating between them at Catherine's behest. Catherine and Marita continue to have romantic interludes of their own, and all three swim nude together daily.