I don't know how you get there; only that you do. It is by no means sudden, but at the same time, it was suddenly one day that I realized I didn't feel a nagging need for him anymore. One day you will look back and realize that one year ago today you were a lot more of a train wreck than you are now--that you were calling him in the middle of the night sobbing, begging him to take you back. And on this day you will finally be able to feel so grateful that you were privileged enough to experience love like that, instead of simply wondering why it had to end. You will think of those memories with joy instead of sadness.
And particularly, when you hear that one song--during the which he never fails to appear in your memory, uninvited and unannounced--it is suddenly bearable, and you remember why you liked the song in the first place, before all that whirlwind love and heartbreak made it into something else.
I don't know why or how it happens. It does not rely on conscious decisions or deliberate thought processes. Unfortunately, these things cannot dull the pain as one might like them to. All I know is that time is a friend, a friend that gradually works on you, and so slowly that you couldn't possibly notice. A friend that takes all the tears out of you and in them dissolves the vividity of the images in your head. A friend who seems often cruel, but who, after a long stretch of himself, shows that he loves you enough to mend your heart.