The first stage in relationships is that of dependence, and often co-dependence. In these relationships, one partner (typically the man, or the more masculine partner) is clearly superior and directs the relationship. This type of relationship relies on dominance and submission, which can often lead to abuse. It's an immature type of relationship and is quite unbalanced. It worked well in pre-feminist America, and continues to work for women (and occasionally men) who want to be taken care of their whole life and don't mind putting up with inconveniences to feel the sense of safety they experience.
The second stage is that of independence. The women's rights movement ushered in the second stage in relationships, which balanced the scales in the relationship. The second stage is all about give and take, "you make dinner and I'll do the dishes", everyone getting what's fair. The problem with this stage is that someone is always keeping score, and life isn't always fair. The second stage of a relationship takes a merchant's view of love. Love is seen as a transaction, with something gained and something lost in each exchange. This is, imho, a huge improvement from the first stage, but it left me feeling pretty empty. In this transaction based relationship, we always seem to be trying to change our partner, making suggestions for improvement that of course would help them be happier, in our opinion, but trying to change another is a fool's game.
The third stage of romantic relationships is one of interdependence. It's been called "spiritual partnership" and "conscious union", among other names. The third stage is about what I call "both, and". In this stage, we return to love for love's sake. We stop keeping score, and we understand that "equal" does not mean "the same as". We begin to understand that in order to be authentically engaged in a romantic relationship, we first must be authentically ourselves. We have to be willing to look deeply into the mirror and embrace ALL of who we are. This third stage of a romantic relationship is a coming out of sorts. We have to stop hiding who we really are and embrace the paradox: In my case, a couple of years ago I was confronted with "I am a strong, independent woman who is terrified that the love of my life will abandon me (so I'll leave him first)." I had to embrace that I was both a strong independent woman and someone terrified that love would abandon me. The second created the first. To deny the second would be to negate the first. They existed together both enriching my life and making me feel like a neurotic wreck, until I could come to the place in the middle, honoring both and still find ways to be happy.