The "relationship" lasting longer is not the immediate goal. {;^ )
Speaking as a bachelor, I have found so many damaged and duplicitous women that I find myself preferring widows to the profile of a typical Big D veteran; I have dated a number of cheating married women, until I was so informed (with adequate evidence) or discovered "the sinner". I am thankful that women can stand men as men are surely worse still than women in such matters.
The "Sex in the City" relationship model is as if STDs designed it for themselves.
One might surmise that even with today's astounding population densities, the proportion of lonely people today may only equal those of centuries gone by. Still, as a practical matter, plural "marriage" may be a lasting arrangment as I believe that there are more good women than good men - as this author verbosely beat around his bush.