Darwin was a 30 year old Victorian virgin who imagined that human sex took place in ways that conformed with the social mores of his time. As someone who was in a monogamous marriage for 20+ years and who is now (with that same man) in a variety of polyamorous relationships, I can tell you from experience that jealousy and the desire to "drive others off from your cow" is a learned, societal one. It's a scarcity mindset that comes out of the patriarchal system, which you have correctly identified entails much more than a power imbalance between men and women.
As I touched on, many modern cultures who have social monogamy do not subscribe to sexual monogamy. Here's more about that:
Pair Bonding Is Ancient; Sexual Exclusivity Is Modern
For many humans, being married was never about just one sex partner
A more apt term for patriarchy coined by systems scientist Riane Eisler is domination system (as distinct from partnership system, which is what egalitarian societies lean towards). This reflects the hierarchy of power that is maintained through fear and coercion, as well as a sense of obligation to the system - much like a feudal one. Although, creating a system that controls and polices female sexuality is central to creating a dominance hierarchy, it isn't the only feature of it - something that I've written perhaps 20 stories about.