Tsuki to Mizuumi
From Shogakukan:
Kazuna's late grandfather was a writer, and his unpublished novel depicting his private life was found among the articles left by him. He had written down his affection to his lover, while he was a devoted husband. Kazuna felt perplexed, and went to see his grandfather's lover. Hinako Ashihara depicts sweet, painful love in this collection of her long-piece love stories.