The idea of abandonment (such as physically leaving, or neglecting a responsibility).
You leaving someone can also represent: a decision (perhaps a decision to end a process); standing up for yourself to make needed changes in your life.
Someone leaving you can also represent: a feeling or fear of being abandoned, alone, or left behind in real life.
See also: Abandonment; Leaving a Place; Betrayed, Being; Betraying; Rejection; Escaping; Goodbye; Distance