Impulsive, fickle (10)
I believe the answer is:
capricious
I believe this clue is a double definition.
'impulsive' is the first definition.
(I know that impulsive can be written as capricious)
'fickle' is the second definition.
(thesaurus)
(Other definitions for capricious that I've seen before include "Arbitrary and inconsistent" , "on a whim" , "Given to sudden mood swings" , "Changeable in mood" .)