Unfaithful (6)
'unfaithful' is the definition.
(associated in meaning)
This is all the clue.
(Other definitions for disloyal that I've seen before include "Treasonable or treacherous" , "Deserting allegiance or duty" , "Unfaithful or unpatriotic" , "The opposite of 11 Across" , "Not faithful, unpatriotic" .)
'unfaithful' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for fickle that I've seen before include "Erratic, unpredictable" , "Having changing loyalties" , "Liable to sudden unpredictable change" , "Prone to shifting loyalties" , "Subject to changes of mind" .)