To get an informed opinion of what co-dependency is, read the book "women who love too much" by Robin Norwood.
Women Who Love Too Much: When You Keep Wishing and Hoping He'll Change by Robin Norwood 4.02 · 
This text is suitable for the reader for whom being in love means being in pain. Therapist Robin Norwood describes loving too much as a pattern of thoughts and behaviour which certain women develop as a response to problems from childhood.
Well, not just women, actually. What's with the sexism here?
However, what people attribute to the word often misses the point. Really, read the book if you're interested. Supposedly a free version here: