Empathy, love, respect, understanding... we can write dozens of things here. I think the first thing that both people should have is a good way of perceiving the moment. because this situation allows two people to analyze the moment, the situation and the turmoil they are in. When you see a couple fighting, one tells something and the other tells something else, they are not aware of the situation they are in, the situation, the other person. You have to understand the person, the moment and yourself. This is the most principled.