In 1833, Abraham Lincoln was a 24-year-old postmaster in New Salem, Illinois. His friend Elizabeth Abell introduced him to her sister, Mary Owens, who was visiting from Kentucky. Afterward, he remarked to Abell that if Owens were to return to Illinois, he'd marry her. It was most likely a throwaway line, but Abell told Owens, and she paid another visit to New Salem in 1836, considering herself therefore engaged. By then, Lincoln was not at all on board with the idea of marrying her. He wrote to another friend:
“I knew she was over-size, but she now appeared a fair match for Falstaff. I knew she was called an ‘old maid,’ and I felt no doubt of the truth of at least half of the appellation. But now, when I beheld her, I could not for my life avoid thinking of my mother. And this, not from withered features, for her skin was too full of fat to permit its contracting in to wrinkles; but from her want of teeth, weather-beaten appearance in general, and from a kind of notion that ran in my head, that nothing could have commenced at the size of infancy, and reached her present bulk in less than thirty-five or forty years; and, in short, I was not all pleased with her.”
To be clear, Owens was the same age as Lincoln. Lincoln was not so brutally honest with Owens, but neither did he diplomatically break off the "engagement." Instead, he corresponded with her about the dire circumstances she would find herself in if they married. His ruse worked so well that Lincoln himself suffered from the way the relationship ended. Read the story of Abraham Lincoln and Mary Owens at Atlas Obscura.