Is "Emotional Pain Addiction" a real phenomenon, a legitimate concept?
Emotional pain can become an addiction. A negative feeling, such as anger, worry, grief, fear, or depression, can become so habitual that you cannot live without it. There are physical as well as mental reasons for emotional pain addiction. When a person is continuously stressed by emotional pain, there are subtle changes in the body that create a dependency on stress-related chemistry. Changing habitual patterns of pain can be as difficult as giving up an addictive substance, such as nicotine, alcohol, or even heroin. The emotional pain addict unconsciously seeks out situations that are sure to result in pain. A history of prolonged, negative, stressful relationships is usually symptomatic of emotional pain addiction. (http://www.thepositivemind.com/poetry/aboutpainanddullnessarticle.html)
We can find many informal discussions about "Emotional Pain Addiction" on Quora by non-experts, and also presentations by self-development coaches on their websites, but also some apparently more scientific stuff here and there, in particular explaining the functions of endorphins (e.g. , ,  below):
Yet, a simple query on Google Scholar gives you no scientific research outputs on "Emotional Pain Addiction":
And the apparently more scientific stuff on "Emotional Pain Addiction" can be self-contradictory, because  says it is possible to be addicted to endorphins, while  says it is not possible to be addicted to endorphins.