It is OK to hurt over things lost, or things time has changed and separated from what it was you once knew. In fact, it is productive to do so. It is wrongβ detrimental, even, to believe one must run from hurt such as this. Memory and mistake often come one wrapped within the other, thus to grow and learn one must take them both in hand and embrace them as old friends.
Throughout life, the list of memories and the list of mistakes grow. Acquaint yourself with them. Look backwards and wave fondly at each as you strive further and further up the path away from them.