I've just read The Perfect Affair by Claire Dyer. A well considered and easy read, thoughtfully constructed. Claire came to the book group, and it was interesting to hear it discussed. I would add that having read the book, I think there should be a sub-title identifying that the marriages end honourably! Heartwarming, not corny!
For a classic, Truman Capote Breakfast at Tiffany's, short, delicious and engaging. I fell in love with Holly.