"I hate myself for loving you" - Relationship question?

I heard this song by Joan Jett yesterday. I have never been in a relationship of this nature and wondered about them.

Have you ever been in a relationship that, although you realized it was bad for you or going nowhere, you just could not bring yourself to give it up?

If so, why?

Why did you stay? What did you get out of the relationship? What was it about the other person that kept you hanging on? Were they that good at manipulating your feelings or were you that insecure that you did not think you could do better?What did you get out of it (negative or positive)? Did you eventually get out of it? How did you finally leave by yourself or with help? Did you learn and not make the mistake again?