Closure

What it is about the breakup of relationships that makes us feel the need for closure? I spoke to my ex today for the first time in over three weeks. She felt this need for closure and said that since I talked to her it broke that feeling of closure for her. The weird thing is that I actually feel a sense of closure after I talked to her. I understand that our life paths are heading in different directions and it makes me feel sad. But at the same time, I have this strange sense of calm and understanding. A part of me appreciates the calmness, but a part of me feels completely empty. The realization of the relationship being over may be more than my brain can comprehend at the moment. All I can do is appreciate the calmness right now and hope that it lasts for a while.