We are creatures of habit. We like stability. So changes are hard.
There are few things in life that are certain and change is one of them.
In Buddhism this is known as impermanence. It is the truth that nothing lasts, nothing stays the same.
But sometimes change is good news. Sometimes it means the beginning of a new job, or a new house.
Then we need to be careful of our expectations. Sometimes a new relationship is not as good as a past one.
The key is non-attachment.