I think 'A Farewell to Arms' tops the list. The way Hemingway writes about the love between the main characters is just captivating. It's not just a simple love story; it's about two people trying to find love and meaning in a world torn apart by war. 'For Whom the Bell Tolls' also has a significant following. The relationship in it is a key part of the story, and it shows Hemingway's ability to weave romance into a tale of war and struggle.
One of the most popular is 'A Farewell to Arms'. It's a love story set against the backdrop of World War I. The relationship between Frederic Henry and Catherine Barkley is complex and poignant. Another popular one could be 'For Whom the Bell Tolls'. While it's more about the Spanish Civil War, the relationship between Robert Jordan and Maria has elements of romance.