Actually monogamy is not a human thing, in fact most mammals are not monogamous. They don't mate for life. Men, by nature, will try to have as many mates as possible to make sure their genes are passed on. Women tend to "nest". Even gay persons are the same in this manner.
Monogamy is a human thing, as a matter of fact. While mammals may not be primarily monogamous, humans evolved beyond the primal instincts of the wild because they conflicted with the growth of law and order... civilisation. Early primitive man may have given in to his carnal urges and sowed his wild oats anywhere and everywhere he could, but civilised man saw the error of those ways in a structured society. For example, the wild a free copulation of one generation could affect the next generation, in that people wouldn't know who their brothers and sisters were.... and you know of the dangers of inbreeding within humans, don't you.
So yes, monogamy is a human thing, it became a necessity and is preferred because human emotions become to complicated otherwise. Sure, some societies practice polygamy, but in most instances the women in multiple wives relationships are are subjugated and know no better because they have little or no access to education and have no knowledge of alternative societies/cultural beliefs
Men, by nature, will try to have as many mates as possible to make sure their genes are passed on.
Please don't include me in that! I don't feel the need to procreate whenever, where ever possible, and I would still be with my first wife if she hadn't found family life such a difficult prospect. I've been remarried twice since then, but not to procreate, not to primarily exercise my carnal urges, and not to satisfy any lusting. That's the trouble, see, too people many place too great an importance on sexual matters and neglect to look deeper, whereas I tend to look for companionship with mutual love, trust and respect, similar interests and the willingness to sacrifice personal wants to give as well as receive. This does not mean that I have never been a sexual being. I have been that, when appropriate and the feelings are mutual with the one I love, but I don't believe it is the be all and end all of a relationship.
Is this a moral thing? To a point, perhaps, but it's more something I need to be to feel like a half decent human being. There was a time in my youth when I'd "shag" myself silly because all my mates said that's what they were doing. It was the done thing... and it was expected of me back then, and not just by my mates. Even the girls expected that I should, but I can see now that there was no love and little respect, and now I am ashamed of my actions back then. Yes, the girls may have wanted it, but it was still selfish and if I'd had any self respect, respect for them, I would have told them no.