A good place to start would be Ernest Hemingway's, "A Farewell to Arms". Based on his own experiences, it's about an ambulance driver in WW1 Italy falling in love with a British nurse. You may know about this already.
You can also try and find some books by Luigi Pirandello. "Il Viaggio" (The Voyage) and "L'Esclusa" (The Excluded Woman) are both turn-of-the-century tales involving one woman and two men.
Hope this helps.