My Dad sent this too me after I broke up with my girlfriend once again (haha).
When making significant life changes, you should expect many of your relationships to be damaged or concluded.
This is true for any significant life change, whether it be positive or negative. Many of your preexisting relationships will no longer function as smoothly as they did before or they will completely end. Simply put, this is because those relationships were built upon your personality before the change.
While this is not necessarily a bad thing, it is important to realize that this is not a failure on your end nor is it indicative of your life change being negative. It is simply a fact of life and during positive changes it often removes negative or toxic people from your life.