Another theme could be growth and change. As time passes, the 27 old lovers may have changed in many ways, and the story could explore how these changes have affected their views on their past relationships. It might also show how they have grown as individuals and how those past relationships have contributed to that growth. For example, they may have learned important lessons about communication or self - respect from their failed relationships.
The theme of memory and its power is also likely. The story could be centered around how the memories of these old lovers still linger. These memories could be both beautiful and painful, and they might influence the characters' current lives, relationships, and decisions. The characters might be haunted by the what - ifs or might find strength in the positive memories of their past loves.