“All marriage is such a lottery -- the happiness is always an exchange -- though it may be a very happy one -- still the poor woman is bodily and morally the husband's slave. That always sticks in my throat. When I think of a merry, happy, and free young girl -- and look at the ailing aching state a young wife is generally doomed to -- which you can't deny is the penalty of marriage.”

Source: Smooth Talking Stranger

Source: Love in the Time of Cholera

Advice to a Young Man on the Choice of a Mistress https://www.swarthmore.edu/SocSci/bdorsey1/41docs/51-fra.html (25 June 1745)
Epistles

Thoughts on Various Subjects from Miscellanies (1711-1726)

Letter to Mrs. Bryan Waller Procter (26 November 1856), from The Letters and Private Papers of William Makepeace Thackeray, ed. Edgar F. Harden [Garland Publishing, Inc., 1994, ISBN 9780824036461], vol. 1, p. 763.

Source: The Note Book of Elbert Hubbard (1927), p. 54.

Letter to Michael Tolkien (March 1941)
Context: Nearly all marriages, even happy ones, are mistakes: in the sense that almost certainly (in a more perfect world, or even with a little more care in this very imperfect one) both partners might be found more suitable mates. But the real soul-mate is the one you are actually married to.