Dhammapada 309, 310

Four things does a reckless man gain who covets his neighbor's wife—a bad reputation, an uncomfortable bed, thirdly, punishment, and lastly, hell. 

There is bad reputation, and the evil way to hell, there is the short pleasure of the frightened in the arms of the frightened, and the king imposes heavy punishment; therefore let no man think of his neighbor's wife. 

IMAGE: William Blake, Inferno, Canto 5: The Lover's Whirlwind, Francesca da Rimini and Paolo Malatesta (c. 1827)