There are very few relationships where both people are equal, but there are compensations they have worked out over time. A spouse who likes to control everything is often a person who finds someone that likes to have others make the decisions. It might not seem this would be anything but an abusive relationship with one person having all the power, but it is equitable because each person receives what they need or want. Between two people building a life together, it is about being able to share in a way that fits both of them.
It used to seem that old-fashioned marriages where the husband worked and the wife stayed home to raise the children were unequal relationships, but it really was dependent upon how their interactions worked for them. Many women had plenty of control and power within their marriage, but it was not where people could see it. They would tell their husbands what they wanted, and the men would generally comply. Choosing where to vacation, how they would spend their money or where their live was headed was often a decision both of them made together.
Marriages and long term relationships today are often unequal on the outside, but the balance of power between two people tends to be hidden still. He might seem to be the boss to the outside world, but she might run his life completely where no one can see. Conversely, the power balance might look the opposite way for another couple. It does not matter as long as both people are satisfied with their relationship and decision making.
There are few issues in life where everything is black and white or measures completely even on a balancing scale, and long term relationships fit with that. As long as both people are happy with their choices, there is equality between them.
