What helped me explain to my husband was to talk about "structural dissociation". Here's a few links (I found the illustration to be most helpful when showing what it means):

http://www.complex-trauma.eu/wp-cont...05/sd-ptsd.jpg
Summary Structural Dissociation | Complex Trauma
Structural Dissociation of the Personality - Dissociative Identity Disorder, Dissociation and Trauma Disorders

One of those articles is rather in-depth but it helped me to understand more about it so I could translate it into layman terms.