And FWIW, even if the sex *stops*, a husband deciding to replace her with somebody else is seen with some degree of social scorn and shame even in modern secular circles. And there's an implied sense that she *supports* him in various ways and should be entitled to *something* if he opts to leave.

There's just far less public, widespread sympathy for the recipient of a sugar daddy's benefits. Her friends might feel sorry for her, but nobody will treat her the same way as married woman going through a divorce.