Negative reactivity between partners is what keeps couples making the same mistakes over and over. That's when one cannot have a negative emotion without the other responding defensively. The principle holds even if the negative emotion is not expressed - one sulks, the other reacts.
From outside this interactive dynamic, it's easy to come up with pop-psychology answers about better communication or boundary-setting. Within the dynamic, it feels more like a struggle for autonomy and the self. It feels that way because they have so much emotional power over each other that neither is autonomous in their choice of thoughts, feelings, or behavior; they just react to each other.
Reversing negative reactivity starts with questions that are more philosophical than psychological. You have to decide what kind of a person and partner you want to be. The couples who come to our boot camps must answer the following questions as a starting point: