I'll contribute just one little thing, since others have offered so much already.
I continually remind myself that how anyone I'm involved with treats me ... is how I'm treating myself. This way I accept my responsibility for sticking around.
The thought helps me to recognize when I'm being mistreated, and that I have the option of not being mistreated. And it helps me see what power I have to choose.
I do not accept mistreatment or abuse. It's simply not acceptable. Yet it will happen now and then, and I have to decide if it is a pattern or just the result of someone having a difficult moment.