[davemo]

The quote in context is: "Husbands and wives may allow their partners to fill the role of best friend, letting other relationships fall by the wayside (something I’ve tried to actively resist)."

It seems the author is advising against forsaking other relationships and placing the entirety of the burden to supply all of our friendship needs on our significant other. I think there's wisdom in diversifying our relationship portfolio the same way we do with investments.