No one could realistically suggest that there's anything easy about having people we care about depart from our lives, by whatever means. I know I can't "shrug off" such things (to my cost). But things change, people change (for better or worse) for whatever reasons, and that quote from "Objects at Rest" simply says that such things are part of everyone's life. "The process is painful, but often necessary", because sometimes to stay just means even more
pain. In any case, it's better to remember the good about the other person(s) and move on. That's difficult...but necessary.