First of all we have to remark here that by nature man is inclined to inconstancy in love, woman to constancy. The love of the man sinks perceptibly from the moment it has obtained satisfaction; almost every other woman charms him more than the one he already possesses; he longs for variety.
 Arthur Schopenhauer, The World as Will and Representation (1819). copy citation

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Author Arthur Schopenhauer
Source The World as Will and Representation
Topic satisfaction constancy
Date 1819
Language English
Reference
Note Translated by R. B. Haldane and J. Kemp
Weblink http://www.gutenberg.org/files/40868/40868-h/40868-h.html

Context

“Now that an instinct entirely directed to that which is to be produced lies at the foundation of all sexual love will receive complete confirmation from the fuller analysis of it, which we cannot therefore avoid. First of all we have to remark here that by nature man is inclined to inconstancy in love, woman to constancy. The love of the man sinks perceptibly from the moment it has obtained satisfaction; almost every other woman charms him more than the one he already possesses; he longs for variety. The love of the woman, on the other hand, increases just from that moment. This is a consequence of the aim of [pg 351] nature which is directed to the maintenance, and therefore to the greatest possible increase, of the species.” source