We can learn much about ourselves from all our emotions and by doing so they can help us grow and guide us in our future relationships. To deny or wish these emotions away is not helpful and flying in the face of your personal reality. If we look out of the window and it is raining, no amount of telling ourselves that the sun is shinning will stop the rain. However, we can tell ourselves truthfully that it will not be raining forever.
What can cause us a problem are some of the things we may do with our emotions when we do not like them or do not know what to do about them. For example, denying that we are experiencing a particular emotion, stuffing it back down inside of us or trying to distract ourselves away from it in some dysfunctional way can cause us problems. But it is not the emotion itself that is the problem, it is what we are are doing with it.
To grow from the emotional experience we need to understand what the sadness is telling us about what we lost really means to us. Understand this and we are then free to move on.