Even if two people have the same score on an intelligence test, they are not of equal intelligence. One person may score higher on communication, but the other is much better at math. Life is full of compromises, and each person must use the intelligence they have to get through life. There are many different ways to apply it, but not all of these ways are of equal monetary value. This fact generally makes one person in a relationship more valuable than the other when it comes to navigating life.
Just because a person is intelligent, this does not make them able to live a good life. They may have issues with socializing or dealing with unplanned events, and it might keep them from functioning on a normal level. They might need a partner to compensate, but they must find a partner who needs them just as much. Balancing their needs and abilities together is the best way to use their intelligence to form a stable relationship that will last a lifetime.