Change happens. "Good" change, "bad" change. It happens. Welcome it. That means that time is working. Accept each change as it is, do not fight it. This will get you nowhere. Be okay with the truth that nothing lasts forever. Even the good stuff. But, in regards to the bad stuff, this helps us to remember that it will not last forever.
It is interesting that we do not appreciate something as much until it is gone. We often realize our mistakes after, but we can learn from them and carry those teachings to new relationships and new experiences.
Just remember. Appreciate what you have now, for one day it may be gone and you will have wished that you were more grateful for it in the moment.
On a final note, the best thing you can do, is to be honest to yourself. Do not lie to yourself by holding onto things. Let it go. There is more in this world. You will learn.