In order to answer this question about the one thing couples do not realize when they are fighting, a little background is helpful. Science from all sorts of fields tell us that loneliness raises our blood pressure and can increase the risk of heart disease, even stroke, by double.
Codependency originated around the early 80’s to help families with alcohol and drug problems. It stemmed from the idea that the whole family system needs to be addressed to achieve recovery, and that certain family members may be hindering the process by enabling the substance abuser. The word and the concept are still wildly popular today, and hundreds of self help books exist to serve you.