It's interesting what happens when you get your heart broken.
Your ego goes either on the defensive or offensive. It never quite accepts what happened.
When it goes into the defensive mode, you sit there and ask yourself, "Why didn't [this person] choose me?" or "What does [she/he] have that I don't?" Then it progresses. "What's wrong with me?" or "No one will EVER love me." We feel so sorry for ourselves. We tear ourselves apart and convince ourselves we're not good enough.
The offensive mode is interesting as well. Our friends help us with this. "[He/she] doesn't deserve you," or "[He/she] isn't capable of having a normal relationship with anyone, let alone someone as wonderful and lovable as you." We tell ourselves that it's THAT person with the problem, not us. We tear the other person apart, demonize them in a way, to make ourselves feel better.
We even try to get status reports. We check the profile on MySpace and Facebook. We ask our friends if there's another person. If there is, we compare them to ourselves.
Then, of course, rather than deal with the pain, we just jump right into another relationship. Our ego seeks out someone who will pacify the insecurities if we're in the defensive mode, or to "one-up" the former lover if we're in offensive mode (this is the "I'll show HIM/HER that I'm better off with THIS person).
But what we ultimately have to do is accept our mistake and forgive ourselves for making it. We must realize that sometimes relationships don't last forever, and the chapter with this person is now over. However, there is MUCH more to this...
We made that choice with the state of consciousness we were in weeks, months, or even years ago. The experiences and circumstances brought you two together for a purpose--for the healing of the BOTH of you.
In this regard, it's not really a "mistake" as much as it is a choice that was made to heighten our awareness of something within ourselves that needed refinement or healing. The key is--we need to acknowledge and accept the suffering that resulted from this relationship, but know that there is a lesson to be learned.
This only can be done alone--with some introspection. Many people don't want to do this. They're so used to being with someone, that they fear the separation. They don't want to drop the attachment because it hurts too much. They don't want to be alone with the pain.
But the pain transforms you. You see, eventually and objectively, where you and the other person "missed the mark." You forgive that person for whatever pain they caused you, but you forgive yourself as well. You see the choices that you made, and see if you've made those choices in the past. You learn to work on those characteristics so you don't make that choice again. You shed a little more light into a dark side you might not have wanted to acknowledge in the past.
And ultimately, you'll see that the relationship did make you a better, stronger person. You rise to a new level of awareness so you don't make the choices that brought you pain ever again.