Monogamous marriage models largely stem from agriculturalization and the need to have sons to inherit land and dowry to obtain wives as a transaction of property to give the man more sons.
Because traditionally, land could only be passed down to male heirs, women were viewed as chattel -- basically objects to be bought and sold like property -- which is why in ancient religions like Judaism and Islam, women were essentially married off to men either in arranged marriages or through dowries.
China also has a long practice of dowries and equating women to property or at least tying up her worth in the ability to be an incubator to produce male heirs to inherit the land of their fathers. Daughters were traditionally sold off to other families.
It's also why, I think you'll find, many world religions emphasize that it should be a man and a woman, or a man and multiple women, who should be allowed to marry and not, for example, homosexuals. Homosexuality doesn't produce offspring to inherit land or sell off and so goes against the oft cited religious commandment to "be fruitful and multiply."
However, in a modern world that is overpopulated, the religious commandment to "be fruitful and multiply" can be seen as dangerous and, at the same time, it places unnecessary financial and economic strain on the families and communities that continue to practice it.
Personally, I think this origin of monogamous marriage being tied up in land and property after the agricultural movement actually leaves lingering side effects. Once example is that many monogamous relationships stemming from this model of marriage view "love" as a possession. "He's mine and I'm his" or "she's my girl" and etc. are all demands set upon love to be an object of ownership.
It usually leads to the objectification of the romantic partner and, with traditional monogamous expectations in place, helps to promote jealous emotions when you expect your property/love to belong to you and only you.
But love doesn't work like that and people are individuals, not property. So, when a person falls out of love or the relationship fails, for whatever reason, feelings of jealousy grow exponentially and often times "cheating" occurs. Because, of course, in a monogamous model anything beyond the initial pairing of partners is forbidden.
But that's approaching love in the wrong way. Because the truth is, people can love more than just one person and have the right to be loved by more than just one person.
To restrict love to a possessive form of jealous ownership is a bad relationship model, in my opinion. It's why divorce rates are so high.
After the relationship starts to break down, people begin to search for love elsewhere. And that's a natural human desire -- the desire to be loved and have a fulfilling relationship with a life partner that truly understands you.
Sometimes a monogamous relationship can trap people who have fallen out of love, so to speak. Because of all the cultural and social expectations placed on them to be faithful to one another.
It's an unrealistic ideal. And it ignores other relationship models such as polyamory which actually resolve many of the possessive attitudes that can hinder healthy marriages by creating a sense of ownership over the other person and replacing acceptance of one's needs and feelings with outright jealousy.
Having said all this, I am married. I am not monogamous myself, but my wife is. Simply put, there are many different ways to approach marriages and relationships -- but the key is being open with your partner and expressing your desires. If they can't accept you for who you are and constantly deny you the right to exist as the person you know you are, then they are not a good partner and that relationship is doomed from the start.
But if they communicate and work with you and give you the acceptance and understanding you need to thrive as an individual, then they may be a keeper.
That's just my two cents.