One theme in Guy de Maupassant's story "Moonlight" is recognizing the difference between loving someone and loving the idea of love. A second theme concerns the inherent struggle between withholding or revealing information that may hurt someone.
While on vacation with her husband in Switzerland, Madame Henriette Letore has an affair and doesn't know if she should tell her husband. Her guilt manifests as two white streaks in her hair. Her sister, Madame Julie Roubere, demands to know what caused her hair to turn white. Despite her shame, Madame Letore confides to her sister that she took a lover one night while on vacation.
She explains that she decided to have an affair only after her husband turned down her advances. She didn't set out to have one, she says, but was overwhelmed by how beautiful Lake Lucerne appeared in the moonlight. A young man found her that night and talked with her, showing her the attention her husband had long denied her. Madame Letore blames her husband's indifference for her affair, but her sister suggests that his indifference had nothing to do with it. She suggests that Madame Letore didn't have an affair with the man as much as she did with the idea of being loved and desired. To help ease her sister's guilt, she suggests that she actually took the moon as her lover.