Codependence is when someone becomes involved with and manipulated by someone else who has an addiction, or a psychological disorder. The codependent becomes involved to the extent that they begin enabling their partner's condition by, for example, making excuses for their behavior. The codependent may feel guilty when s/he has thoughts or feelings that conflict with the interests of their partner.
Codependence (or codependency) is a popular psychology concept popularized by Twelve-Step program advocates. A "codependent" is loosely defined as someone who exhibits too much, and often inappropriate, caring for persons who depend on him or her. A "codependent" is one side of a relationship between mutually needy people. The dependent, or obviously needy party(s) may have emotional, physical, financial difficulties, or addictions they seemingly are unable to surmount. The "codependent" party exhibits behaviour which controls, makes excuses for, pities, and takes other actions to perpetuate the obviously needy party's condition, because of their desire to be needed and fear of doing anything that would change the relationship. _Wikipedia