"My husband and I both date other partners, and we've been doing so since before we were married."

"It was our first choice of approach for the relationship (not a fallback position). Initially we both dated relatively casually outside of our marriage, although I started seeing someone about a year ago with whom I unexpectedly fell in love. These days I am only seeing my two lovers, while my husband continues to date other people causally."

From a Slate article by Carrie Ichikawa Jenkins titled "How Do You Maintain Desire in a Long-Term Relationship? Date Outside the Marriage." Jenkins and her husband are both — she says — "professional philosophers."

Some people stay single because they love dating. Some people get married and think finally, no more of the ordeal that is dating. And then there are the "philosophers"....

ADDED: Jenkins writes that her "husband continues to date other people causally." Philosophers are careful with language, I think, so I take that to have something to do with the processes of cause and effect. We are talking about relationships. And the expression "causal relationship" is common. But it's possible that Jenkins got careless, like that time she "unexpectedly fell in love," and maybe she meant that her husband "continues to date other people casually," which is nice for her, since that crazy thing called love is annoying when your spouse does it with someone else when you are dating "Accidentally... Without design or previous intention; as it happens or happened; by mere chance" — (to use the OED definition of "casually").

1828 C. Lamb Poor Relations in Elia 2nd Ser. 149 He casually looketh in about dinner time.