Fitness is for getting away from Other Half (6)
I believe the answer is:
health
'fitness' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for health that I've seen before include "Well being; a toast" , "Fettle -- condition" , "Fine condition" , "Physical welfare" , "good shape" .)