faithless

Synonyms: capricious changeable changeful cheating deceitful dishonest double-crossing double-dealing doubting dubious false fickle fluctuating inconstant perfidious recreant skeptical traitorous treacherous two-faced two-timing unbelieving unconverted unfaithful unloyal unreliable unstable untrue untrustworthy untruthful wavering

Antonyms: believing faithful constant loyal reliable true