Death Do Us Part, by Robert Silverberg (epub/Kindle/pdf)
This modern classic of science fiction—first published in 1996—has been reprinted more than 15 more times since its original appearance, including in a Year's Best volume.
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It was her first, his seventh. She was 32, he was 363: the good old April/September number. They honeymooned in Venice, Nairobi, the Malaysia Pleasure Dome, and one of the posh L-5 resorts, a shimmering glassy sphere with round-the-clock sunlight and waterfalls that tumbled like cascades of diamonds, and then they came home to his lovely sky-house suspended on tremulous guy-wires a thousand meters above the Pacific to begin the everyday part of their life together.
Her friends couldn’t get over it. “He’s ten times your age!” they would exclaim. “How could you possibly want anybody that old?”