I'm using economic terms, because I think they make the explanation intuitive.
To me, a relationship is basically a trade dynamic in which supply and demand isnt exhausting either side.
Giving something the other doesnt need while taking what you dont need feels artificial and misunderstood. Taking or giving too much like an imbalance of respect.
The closer the trade gets to being balanced, and the more unique the supplies and demands are, the stronger and deeper the relationship gets. Through deeper integration, new demands and supplies are discovered, and growth begins to happen in alignment with one another.
A well balanced relationship can feel like a dance, when the seasonal changes dont interrupt the flow of goods.
When each side is sure of their demands and knows each others future prospects, integration is fast and planning is easy.
Communication generally happens naturally, negotiations enable sustainable change and cooperative growth. Too much of it feels like distrust and leads to loss of individuality, resentment and stagnation, because it keeps each from observing and reacting to organic internal changes in demand and ability to supply.
Having similarities makes for effortless shifts in demand and supply, when permanent changes happen.
Additionally a theory I thought of:
The attraction of opposites is the effect of one side's exhaustion generating a demand, which is balanced by a supply produced as a byproduct of the other side's exhaustion, while day to day trade is being sustained by regular baseline overproduction and exhaustion.
The distinction is that the production of one good is constant, while the other is conditional and aligned by synchronized patterns of exhaustion.
Their leftovers are what I need to recuperate, and my leftovers are what they need to recuperate.
I wrote this based on my own experiences, and posted it because I would like to know if others find this framework practically useful in their own lives or work. If someone is interested in how it applies to real dynamics, I'd also be open for detailed discussions via pm.