Refined models say that selection favors our looking for new partners while in relationships and to allow our partners to do the same. Non‐looking is only expected to evolve if there is an extremely large cost associated with being left by your partner

Can Strategic Ignorance Explain the Evolution of Love? Adam Bear, David G. Rand. Topics in Cognitive Science, https://doi.org/10.1111/tops.12342

Abstract: People's devotion to, and love for, their romantic partners poses an evolutionary puzzle: Why is it better to stop your search for other partners once you enter a serious relationship when you could continue to search for somebody better? A recent formal model based on “strategic ignorance” suggests that such behavior can be adaptive and favored by natural selection, so long as you can signal your unwillingness to “look” for other potential mates to your current partner. Here, we re‐examine this conclusion with a more detailed model designed to capture specific features of romantic relationships. We find, surprisingly, that devotion does not typically evolve in our model: Selection favors agents who choose to “look” while in relationships and who allow their partners to do the same. Non‐looking is only expected to evolve if there is an extremely large cost associated with being left by your partner. Our results therefore raise questions about the role of strategic ignorance in explaining the evolution of love.