Co-dependency

Codependency is a psychological condition that makes the person put the needs of others before their own. It originated to describe people in a relationship where they become care-givers to someone who has a substance abuse problem (eg an alcoholic or drug addict).
In a codependent relationship, individuals put the other person’s needs before their own, often sacrificing their own integrity and sense of self in the process. Codependency can cause a person to have an overinflated belief that they alone are responsible for affecting the beliefs, thoughts, emotions, and behaviours of those around them.
So codependency is a word used to describe a person who is excessively focused on taking care of the needs of others. This behaviour leads to them having problems in their life because they never do anything for themselves, but they exist to serve their partner. They feel guilty or ashamed whenever they do something for themselves, so they neglect themselves.
Unfortunately this means that codependent people are easy targets for abusive people, especially those who have narcissistic personality disorder. They often end up in relationships with people who have NPD, because narcissists have an extreme need for admiration, which the codependent partner is very willing to provide.
Causes of Codependency.
While childhood abuse, traumatic experiences, and exposure to narcissistic behaviors of parents and/or partners seem to play a role, it is difficult to predict codependency on the basis of any of these factors alone.
Symptoms of Codependency.
There are two main forms of codependence: passive and active. Someone who is passively codependent is more likely to avoid conflict and confrontation, going to great lengths to keep things smooth and not rock the boat. Active codependency is often more manipulative, and an individual may try to push their partner into behaving a certain way in order to fill their own emotional needs. 
Both forms of codependence have many things in common, however. Some common signs of codependency include: