The clearest example of pure monogamy is the following scenario:
Prearranged marriage at the earliest age. Sexual unfaithfulness enforced under the threat of death-penalty, social unfaithfulness (not standing by your man/woman) enforced by severe beatings. Finally, if one of the partners dies, the other should be chucked into the funeral pyre as well.
Now, the most brutal thing about this scenario is not the image it provides - but the ruthless efficiency.
Such an extreme form of monogamy fulfills its purpose with perfection:
Monogamous marriage is not as much a contract between two individuals as it is a contract between the two individuals and the collective society.
This scenario provides enormous security; everybody knows how they will live their lives and don't have to wonder about their place in the universe. Order above chaos - the collective fears of the unknown are eased.
In other words, it's the "I don't know how fucked up I am because everyone else is equally fucked up as well. I'm normal!" syndrome.
The prevalent form in the society of today is serial monogamy: you may be in romantic/sexual relationships with more than one partner - just not at the same time.
This form of monogamy is much less extreme: divine predetermination is replaced by concepts of ownership, and deception replaces much of the physical violence. The most direct products of serial monogamy are divorce and the idea of 'cheating'.
The collective fears are mostly at ease, but now there is more room to play.
Just what is so attractive about monogamy and other forms of relationship which rely on dependence?
It tremendously eases self-definition: "I am that which is bonded to that other person."
It's a shortcut to determining who you are. It's not too joyful or fulfilling, but at least you can avoid facing your fears and the responsibilities of being conscious.
Most of what I said above deals with monogamy and serial monogamy as states of mind. I find that the world-views most commonly attached to these forms of relationships are dangerously unhealthy.
However, if we approach these forms without the common mindset involved, then they are just that - forms. Neither good or bad, the usefulness, value, or attached meaning are determined by the individual users of these forms.
If you desire security, thread very carefully in your quest because it may turn out to be the opposite of what you wish for.