We all agree that human monogamy is not "natural" in any animal sense. It's a stretch. If marriage matters to you, and you've been married over a year or ten, this could a pretty useful talk, and takes the topic further and more intelligently than the supermarket magazines ever will.
Just one of the secrets seems to be experiencing one's spouse in different situations and seeing them being effective or impressive in different ways - socially, professionally, intellectually, adventurously, morally, humorously, physically, talent-gifted, etc. We can never know everything about another person and it is much easier to become familiar with a spouse's flaws than with their varied strengths, many of which may be hidden from us.
For one example, when on occasion I have barged into my husband when he is deep in prayer, I do see him with new eyes. For another, when I see him regaling people with wacky stories at a party.
The secrets to desire in a long-term relationship: