From where do we get the expression, 'One night with Venus gets you a lifetime with Mercury'?.

From the 17th Century, before antibiotics, when syphilis was an incurable disease and the "best" treatment was calomel (mercury chloride), which posed its own problems when used over a long term.

Playing off the names of the Roman gods, "one night with Venus" (i.e., one night with a beautiful woman, as Venus was) would be enough for you to contract syphilis, after which you'd have to spend "a lifetime with Mercury" (the liquid metal, not the god or the planet).

https://www.wondersandmarvels.com/2012/03/one-night-with-venus-a-lifetime-with-mercury-syphilis-and-syphilophobes-in-early-modern-england.html