In 1987, psychiatrist Timmen L. Cermak proposed that “codependency” be included as a personality disorder in the American Psychiatric Association’s handbook, the DSM-III. The APA rejected his proposal, concluding that, unlike substance addictions such as drug dependency and alcoholism, what’s often referred to as “love addiction” is not an illness.

Nonetheless, the term has gained currency; now it’s as much a subject of self-help books and magazine quizzes as relationship counseling and psychotherapy. Cosmopolitan’s “9 signs you’re in a codependent relationship” listicle last year ran through a range of dysfunctional relationship dynamics that, to a greater or lesser extent, we’ve all witnessed and worried about in friends or in ourselves, including fear of aband...