As a lifelong co-dependent and apparent sucker for abuse, it took me FOREVER to arrive at this simple answer to all who have taken advantage of my kindness and understanding:
Don’t be afraid to lose someone who is not grateful to have you.
As I head towards 70 years old I find that I have taken abuse from far too many in my life, first from a supremely judgmental family and then just about everyone else I met along the way. From the beginning, when I felt like I must take care of my mother’s emotional needs, I tried to comfort, mediate with and please others instead of standing up for my own needs. In fact, I hadn’t the slightest idea what my own needs were. After years of counseling, I still sometimes struggle with that…

The main sign of codependency is consistently elevating the needs of others above your own. Other signs include controlling behaviors, self-sacrifice, and fear of rejection.
Yes, gigantic fears of rejection and abandonment! And I was certain that if I was honest and truly myself, no one would want to be around me. I learned this behavior from my mother, who worshipped my father, but was also super angry at him most of the time. She thought having her own opinion or interests would be far too selfish, so she took on my father’s interests instead for most of her life, doing things she has no real interest in to please and be with him. After my father’s death she seemed lost. She had lost her leader.
What a shame and a waste of her unique personality and charm. Years of counseling and reading have helped me wake up to my own personality and charm, but also I find now I have a very low tolerance for abusive people. A number of people who used to be in my life are no longer welcome, because I have such a low tolerance for abuse and nastiness. But why should I fear losing them if they were never grateful to have me in their life?
I know it seems late in life to come to these conclusions, but at least I finally got it.