One Swallow Does Not Make a Summer(1947)

Original title: En fluga gör ingen sommar

When Inga Brantemo goes on a business trip to Italy, her husband Bertil gets romantically involved with Christina Lovén, whose father is a book publisher. When Inga returns, Bertil has a difficult time trying to explain who the woman the neighbors saw in the Brantemo home was. Bertil is an author and it doesn't get easier when he and his wife gets invited to Christina's father to talk business.