A lot of people here are posting from personal experience. Codependency varies on how it manifests from person to person. There are a a lot of books written on it, and I would suggest looking into it if you think you might be codependent.
One of the biggest downsides to codependency is the inability to create/maintain boundaries. It can result in being walked over, abused, and never getting what you need. Lots of books of boundaries as well.
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