Once they have been affected---once "it" sets in---codependency....

“ Once they have been affected---once "it" sets in---codependency takes on a life of its own. It is similar to catching pneumonia or picking up a destructive habit. Once you've got it, you've got it.If you want to get rid of it, YOU have to do something to make it go away. It doesn't matter whose fault it is. Your codependency becomes your problem; solving your problems is your responsibility. ”

Melody Beattie

From : Codependent No More: How to Stop Controlling Others and Start Caring for Yourself