I agree with your study. I think monagomy is unnatural. It is a culture of society, things people started to do. I think biblical times and Christianity has a lot more to do with it than we think.

agreed!

It depends on your beliefs. Personally I believe in the traditional guy and girl relationship. I think that if it were natural to have poly relationships you would see it a lot more prevalent throughout history.

Some people are wired for monogamy, some for poly. Whatever makes you comfortable.

Monogamy works for some people and is natural, polyamory works for others and is natural.
I think it's just another one of those things that has multiple sides. There is so much grey area, and that's okay. You figure out what works for you, and then go with it. That's natural. You don't have to be just one or the other.

I don't believe we were necessarily destined or designed or intended to be any specific way.

I actually specifically believe that monogamy is a natural relationship for humans (though not all) -- as organisms that reproduce with a quality of quantity 'strategy', investing 2 parents in the care of the off spring is effective. But culture plays a strong role and certainly the definition of '2 parents' is subjective. I wouldn't judge anyone's choices, I just think it makes sense and is seen in many other animals.

Here is the thing what your describing isn't monogamy, it's pair-bonding. Pair-bonding is not the same as monogamy, i.e. extra-pair couplings are extremely common among pair-bonding animals, although in human terms we would call that "cheating". To put the difference in more human terms wife-swappers are non-monogamous but still pair bonded. The cultural concept we call (monogamy pair-bonding with complete sexual exclusivity by both partners) describes a rare mating strategy among animals, while pair-bonding (with describes a wide range of sexual behavior)that is common.

"I just think it makes sense"
It not that it doesn't make sense per say it that there is an unstated and analyzed assumption imbedded in that statement. It makes the sense in the environments we tend to study. Evolution is about adaption to the environment which mating strategy makes the most sense for humans is not fixed and depends on the environment. For example sex ratio, unbalance the sex ratio and pair-bonding will make less and less sense as a mating strategy compared to polyandrous or polygynous strategies depending on which sex got hit.

This question is little like asking is it natural for humans to be blondes or brunettes. Nature likes variety and adaptability, humans have the natural capacity to adapt to many different mating strategies depending on environmental pressures; some environmental conditions are more commonly seen then others thus leading to certain mating strategies becoming more common then others but we as a spices aren't tied to a single mating strategy.

TL;DR: The "natural" mating strategy for human is "what ever works"; what ever works depends on the environment and other factors; however pair bonding approaches are admittedly popular.