The unwritten rule is, if you leave someone, you must leave them all behind. You must take everything with you so there is nothing left for them to keep going back to. If you're going to rip something, let the pain hurt all at once so they can be left alone to heal without your interruption. No one wants to get caught when they have gotten so far.
And, if someone is leaving you, remind yourself that you are not falling behind but merely learning and moving forward. You leave their suitcases in what you used to call home and run. Run as fast as you can before they take it back. You don't turn around for them to open old wounds with new hands, because they are leaving you. You must be left and you must get up to leave as well.