What a strange question.
Does monogamy exist? Of course it does. Am I monogamous? Absolutely not.
I believe that choices in life are most meaningful when they are choices, consciously made rather than accepted as defaults. I believe there are a great many people who have thought about it and decided that monogamy is what's best for them, a great many other people who have thought about it and concluded that non-monogamy in one form or another works best for them, and some folks who don't much think about it at all and are monogamous because they think that's the only option available.
Life is one of those things that gets better when it's lived consciously.