At the outset, I want to say that when I say codependency, I don't mean the extreme narcissist-codependent relationship where one partner lives to please the other just so that they can keep them just because they derive their self-worth from being in that relationship. I am talking about codependency which provides self-actualization, rather.

Maybe, my understanding of codependency is wrong, so please correct me if I am wrong.

What I mean by codependency is that, a relationship where you put your partner's needs ahead of yours, because that makes you feel good. Men are socio-biologically programmed to be the protector and women are programmed to be the nurturers. A man does feel good when he is there to protect his woman and their kids. In being the white shining knight to save the damsel in distress. A woman feels good when she can nurture her man and their kids. All this could be stereotypes, but still these are the stereotypes that shape the personalities of men and women.

Now, if being the protector, not just physically or financially, but also in ways of showing affection, being a listener and being comforting when his wife/lover feels insecure, makes a man feel pleased about himself - that fulfillment that he has achieved what his own image of a man has been - and in continuing to do so forever even when he isn't really feeling like doing it but nevertheless does it, just because he can be pleased with himself, does that count as codependency? Say, if a man gives up on his hobbies for spending more time with his wife, not because she demands it, but because he wants to feel good about being there for her, does that count as codependency?

And for a woman, if being a nurturer is something so fulfilling that she sees herself realizing her own image of a woman by brushing aside her own inconveniences like compromising on career choices just so that she can be available to fulfill her role as a loving wife and mother who is there to take care of the children, etc. does that count as codependency?

In other words, more than deriving one's "self-worth" from being codependent, one can realize "self-actualization", without any resentment when two people are mutually codependent, can't they? After all if they have to resent someone, they should resent themselves for having a certain "self-image" they wanted to live up to. And that they won't be doing, as long as the other partner too fulfills his/her roles.

If this is codependency, what is wrong with it?

Compare this to relationships that need "romantic love" to sustain while there is no codependency. Romantic love cannot last long as it is derived from the other person's appeal to you which will become boring anyway as time goes on. So there is a need to innovate and keep progressing and that is unsustainable in the long run.

Doesn't that make mutual codependency (not the extreme mental condition that results in narcissist-codependent relationships), better than romantic love?

TL;DR: IMHO mutual codependency in mild levels does result in strong relationships that are sustainable for a long time than a whirlwind romance or a narcissist-codependent relationship.