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1.
Someone with a need to have a partner or a significant other in order for their lives to feel complete.
girl: i need a boyfriend, i'm worthless without one, i'm ugly
othergirl: you're so co-dependent
by utter_genius July 13, 2008
 
2.
One who is willing to be abused. One who gets meaning out of sticking in an abusive relationship.
There is no sense talking to Susan about her abusive boyfriend; she is a codependent.
by Cly July 21, 2006
 
3.
Often describing someone who finds all their value as a human being in having a romantic relationship. If they are single, they feel like a total failure and therefore will put up with all kinds of possessive, unhealthy Mr/Ms. Wrongs to bolster their own self worth.

Often seen in high school sweethearts who date all the way through college and into mid-20s. Even though annoyed and bored with each other, they still refuse to break up because they can't stand being single.
Debbie said she always knew Jason wasn't 'the one', but still dated him for 7 years. She's as co-dependent as a barnacle.
by Shumado March 31, 2014