This is a non-scientific suggestion
[Please be open-minded since we're all just trying to help here]
Maybe we can try looking at codependency from a different angle. We are made of the physical body, emotional and spiritual elements.
If biology is the logical step towards understanding the pathway of the physical body, then astrology explains the whole gravity of your personality. Not only does it explains who you are, it also explains how you became who you are. One can only heal when there is an awareness of the root of an event. (There are many psychotherapists that are astrologers as well, a faster way to identify the cause of a trauma or event.)
The placements of Neptune and Pluto between two individuals are highly related to codependency and empath/narcissist or victim/saviour relationships. Know your boundaries and make them known, instead quietly resenting yourself for being submissive to the other party.
Healing might take place after reading a book, meeting someone, witnessing an event. What harm does it do to give it a try?
Codepency from an astrological point of view:
Astrology book suggestion: Alive and Well with Neptune (Bil Tierney)