Some of our simian cousins are monogamous but not for life. I think we are a monogamous species, but we aren't really good at it.

id say its very rare anyway as I find sex an important part of being with a partner its something you got to try with more than one person. you wouldn't buy the first car you test drove

Oh, it's definitely real - for SOME people, not all. I know quite a few long term, happy couples that will likely be together until the end.

When you're younger, usually it takes being with a few different people before you find one that causes you to forget all others - at least for awhile.
Though my Sister and Brother-in-law have been together since they were barely out of their teens, and have been married over 40yrs.

But then I also know many divorced , serial monogamists, players, and never marrieds. Some are content with their lot, others are constantly restless and seeking to change to some other status. And none of these behaviors are gender specific.
And there are some that simply cannot be faithful to anyone, and do best remaining single.

It takes time to find out where your heart lies !

Yes, but both people involved have to commit to it. I was entirely committed to my ex. I never even looked at another guy, thought about another guy. Too bad my ex lied about his commitment. I don’t think this is a “guy” thing, I’ve seen plenty of women do the same. I think just some people lie and say they are so they can get someone to marry them. Maybe they do that because they like the thrill of cheating and they enjoy making their committed partner suffer. I think we need to encourage self-awareness. If we know we don’t plan on being faithful, we shouldn’t tell someone we do. At that point it’s no longer “I’m not a monogamous person,” it is “I’m a liar.” Two different things.