What is a short summary of the story, Love is Not a Pie, in the collection, Come to Me?

In the short story, Love is Not a Pie, a young woman, Ellen, back home to attend the funeral of her mother, Lila, is confused about the life her parents lead with their dearest friend, Mr. DeCuervo. After Ellen and her sister, Lizzie, piece their separate stories together, they realize that their mother is in love with both men who over the years have agreed to share her and periodically, become a threesome. This upsetting reality helps Ellen to realize her true feelings for her fiancé, John Wescott, and she calls off their wedding