I am both pair-bonded with my husband and openly having emotional and sexual relationships with others. It’s the best of both worlds as far as I can tell. No cheating or lying necessary. We both get security, commitment, and stability as well as variety. I think a lot of polyamory is like this.
That being said, I appreciate how you’ve delineated that what is best from an evolutionary perspective is not always what is best for the individual’s happiness.