I was reminded of this as I was talking with one of my friends going through a situation similar to this one. So why does it hurt so bad? There are obviously many responses to this (some dependent on circumstances), rejection, adjusting to change, etc. But what I have noticed, is that more often than not, there is a common underlying cause for the misery that we feel.
Humans were meant for community and we crave intimacy and relationships, whether they are romantic or not. We strive to fulfill this need through many things actually (just look around at our materialistic, addiction-prone society...), and romantic relationships constitute a huge part of this incessant pursuit to love and be loved. This is especially true in our society today, where our definition of "true love" stems largely from the picture painted by the media and pop culture. It shows up in songs, are favorite books, and our favorite chick flicks. I would venture to say that most girls would love to have a "Noah" in their life (in reference to everyone's favorite love story, The Notebook) or an "Edward Cullen" (although, sorry Twilight fans, I do NOT share in your fascination). The reason this kind of love is so attractive to us is because it, on the surface, is perfect and seems to fulfill every need.
You don't have to look too far into this perception of "love" to hit the wall of logic that says it is impossible. Before you write me off as heartless and hardened, listen to my reasoning. What every person is looking for is complete and perfect fulfillment and no matter how hard you look, you will never find a perfect person on this earth. The reality is that people are imperfect and finite, no matter how hard you look for the "right person". Because we crave this perfect and complete fulfillment and need to love and be loved, the temptation to find it all in one person is great--especially when our society accepts and encourages this idea. The unfortunate thing, is that this idea is unrealistic and cannot last. If you put everything into one person, you are setting yourself up for failure. What happens when this person is no longer in your life?
And this leads me back to where we started. I think we hurt so bad and yearn for that person so much because we have misplaced our affections. We have convinced ourselves that if only we could have that person once again, we could be happy and everything would be perfect. We have put unrealistic expectations and security in someone that can never live up to it--and we only hurt ourselves in the process.
So were we just meant to wander around empty and dissatisfied our whole lives? Absolutely not. We were not created with this desire for love on accident. The Love we are ultimately looking for will never be realized in a person. Perfect love and fulfillment can only be found in One--God, the only perfect One that has ever been. He is the only one that can live up to the standards. Not until we have the most important Relationship right, can we ever hope to have our other relationships right. When we put our ultimate security and love towards Jesus, we are free to give of ourselves and pour into others because we are not constantly wanting to use them for our own fulfillment. We are finally able to appreciate them for who God has made them to be, and to prioritize their relationship where it should be--as a wonderful, exciting contribution to our lives, not the center of it.