A deadness occurs in relationships when people are no longer willing to tell each other how they really feel. When people first fall in love they're more willing to do this because they're still getting to know each other and dependency has not yet set in. As soon as it does, though, people often stop sharing their true feelings out of fear of loss.
Shakti Gawain (1993). “Living in the Light: A Guide to Personal and Planetary Transformation”, Nataraj Publishing