What is a short summary of the story, Plausible Deniability, from the collection, You Think It, I’ll Say It?

In the story, “Plausible Deniability,” a man named William conducts an emotional affair via email with his brother's wife, Libby. When Libby puts an end to their correspondence, William feigns indifference, but he is secretly distraught because he has difficulty achieving intimacy with anyone in his life.