Is the desire for fidelity in a relationship culturally conditioned?

I’m just curious…

Perceived cryptopolygamy (texting to another boy/girl behind the partner’s back, ...) is too common to simply say that monogamy is the natural state and that anything else is a deviation.

The thing is: the “cheating” often is emotional, and not sexual in nature. So the Christian American rants of sexual decadence might as well stop here.