Eu acho que isso é Dead Morn por Piers Anthony (1990). De Goodreads :
In the 25th century survivors of the nuclear war must live underground. Their actions must be regulated. Their passions must be controlled.
Love is a crime, and when a man dares to take a lover of his own choice, he must be punished.
It's time for a change and the only way to alter this grim future is to journey back to the past...
And change a few small details.
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