Franklin cheated on her

Eleanor learned that Franklin had been having an affair with Lucy Mercer, her social secretary, in 1918. According to what she later revealed to her friend and biographer Joseph Lash, it was one of the most horrific experiences of her life. When Eleanor discovered a packet of Lucy's letters in FDR's luggage in 1918, she discovered the affair. Despite the societal stigma that was then associated with divorce, the pair gave it some thought but ultimately decided against it for familial and financial reasons. A divorce would have ruined FDR's political career, and they both felt they wanted and needed to keep their marriage going.

The Roosevelts' subsequent emotional and sexual intimacy has been a subject of debate among historians, although most concur that their marriage remained a lasting shared partnership on many levels. They also agree that Franklin and Eleanor underwent considerable changes as a result of the romance. She purposefully broadened the range and extent of her already significant public and private activities as he got more serious personally and politically.

In 1920, Lucy wed wealthy widower Winthrop Rutherfurd, who had six kids. The marriage lasted until her husband's passing in 1944, and they produced a daughter. Despite his promise to Eleanor that he would never meet Lucy again, FDR asked her to attend his inauguration in 1933. After her husband passed away in 1944, the two started dating once more because FDR craved and needed companionship. Eleanor was upset to discover of these meetings, many of which her daughter Anna organized because she was unaware of them. Being informed that Lucy had been present when FDR passed away in Warm Springs, Georgia, in 1945 disturbed her much more. Until her passing in 1948, Lucy called Aiken, South Carolina, home.