One must take a moment to address why it has come to pass that monogamous relationships are a staple of society. I must disclaim my babble here, for I can only truly examine the age group with which I am most familiar: Americans age 16-24. Truthfully, this acknowledgement is proof enough that anything I say hereafter can be deemed false by wiser and more diversely qualified philosophers.
Having said that, I will begin to make my case.
Young adults, such as myself, feel the need to find one partner with whom the majority of events and emotions experienced can be shared. I see two main reasons for this.
~The first reason is that society deems this state of couplehood extremely important. This importance likely stems from the need for reproduction (and the concept of creation by two beings united as one according to the Christian doctrine which has controlled American society since its birth.*) However, it has developed into a symbol of social status. A stable romantic relationship shows the observer that the people involved are mature, adaptable, responsible, and desirable. All of these traits are important to many people in the focus age group. A person with these traits have a seemingly better chance at success in any given area.
~The second reason is simple. Humans are social creatures. Without company, we experience loneliness. Barring some exceptions, this is an feeling that the standard person in the focus age group has experienced. It has been described as a rather unpleasant feeling. Therefore, humans seek company to alleviate the unpleasant loneliness. It may seem rather simple, therefore, that a person attempts to find ideal and exclusive company. Indeed, it is simple. If this ideal company can be established, a person will have immediate comfort whenever it is needed or wanted. Should, however, something other than loneliness preoccupy the person, such as stress from a new job and the resulting lack of freetime, the desire for company diminishes.
Therefore, relationships are only truly convenient should a person adhere to social stigmas and experience loneliness.
*It could be pointed out that modern society does not necessarily require traditional relationships as much as in years past. This is because not only is the American world becoming increasingly liberal, but because of such, Christian values are losing their sway.
I am incredibly done trying to block this out in a neat and philosophical way for the time being. I would like to make revisions at some point, though I cannot guarantee that I am dedicated enough to this rant.
After all, I may very well just be experiencing a personal and temporary emotional struggle.
You be the judge of that.