Sometimes it is called being a doormat.
We feel we are only to be used by others or we are so used to feeling so poorly about ourselves, we just hang on because in a sick way, we feel comfortable. Some are so used to chaos, normalcy scares them, so they go back to what they are familiar with, afraid to let go. So I guess it's all fear based. There's stuff in some of the 'self-help' group and 12 Step groups since this is not rare. Go looking buddy and tell yourself you are worth more. Boost the old self-image and you're on your way.