In my opinion there is no such thing as ‘both partners in a love relationship loving each other equally', nor is there equality in any relationship [including friendship]. For decades now I 've been interested in the power dynamic within love relationships and I observed, listened, read, and thought deeply about this to gain some sort of understanding about what really goes on within relationships.
One partner will always hold more power than the other.
The clearest examples of this lack of equality is found in the sub-culture of BDSM, which covers all of Bondage, Discipline, Domination and Submission, and Sado-Masochism. I carried out a comprehesive two-year study of this world by interacting with many of its practioners on websites devoted to BDSM. I read whatever I could find on the subject, including a brilliant and brilliantly titled book Fuck the roses, give me the thorns. Once I had learnt about the dynamic between Dominance and Submission, I entered into their world in a cyber yet no less meaningful way - I took a slave! Then another. For me it was often role-playing and it was exciting, but it did not fulfill me as I am not, I believe, dysfunctional enough to take it into real life.
Now slavery in this context is consensual, with a contract between Master and slave, and involves the ‘sacred' handing over of power by the submissive (referred to as a subby) to the Dominant (called a Dom). The Master has absolute control over his slave and in real life situations where they share accommodation, the slave, for instance, cannot enter a room where her Master is unless she kneels at the doorway and waits for permission to enter. Usually they have separate bedrooms, but I will not go into more detail about what rituals, practices, and protocols have to be observed when they interact sexually or during disciplinary acts. I will stress that I was never interested in acquiring a real-life slave, although I could have gone to the US and married either of my female slaves.
Dysfunction is obvious in this extreme example of Master/slave. Both, I would suggest, have serious low self-esteem. The dominant partner needs to be validated by having total control over at least one other human being, while the submissive seems to have such low self-esteem that he/she cannot begin to aspire to be treated as an equal - it is a deeply ingrained sense of worthlessness. Validation comes from seeing to all the needs of the Master/Dom/Mistress/Dominatrix, and in having the security and love found in such a relationship. This sense of worthlessness is seen clearly in situations where the CEO of a company, for instance, will go to a Dominatrix for discipline and sexual activities.
It must be pointed out that both partners need this kind of relationship and are fulfilled by it.
But it is the ‘ordinary' love relationship that fascinates me. Since (I believe) no two lovers can love each other with equal intensity, this inequality of affection influences the power dynamic, but is not solely responsible for its development and eventual permanent status. In a nutshell, once you love someone more than you are loved by him/her, you are extremely vulnerable and are well-placed to be dominated.
And the domination, the shift in power, is often a process, is innocuous and becomes potentially destructive to the relationship. For example, a young husband can be manipulated by his bride by a simple "Do X or don't do Y, and you'll be so glad you did!" The promise of something good (and the good graces of the loved one) is very enticing and before he knows it, the poor guy is not watching the rugby final but taking his wife to visit her aged aunt at an old age home instead! This too, is an extreme example but it emphasises how serious this is. Another device is the Dog Box. Now, a guy who loves his wife/girlfriend less than she loves him, will not be too badly affected by threats of being consigned to the dog box, nor of being in the dog box. He would not care enough. But if he loves her far more than she loves him, he is in serious trouble where power is concerned!
It is nice to be nice, and many people who end up being subservient and submissive in a relationship are to blame for their own sorry state of affairs. A husband who is too much of a ‘nice guy' [ and is not naturally submissive] is a prime candidate for a servile, subservient, submissive, (and thus) miserable life.
I've just scratched the surface here but think about what I have written - not many people think about this; no one is formally taught about love relationships and their minefields.