adj. 25B6; adjective
her husband had been unfaithful : ADULTEROUS, faithless, fickle, untrue, inconstant; informal cheating, two-timing.
an unfaithful friend : DISLOYAL, treacherous, traitorous, untrustworthy, unreliable, undependable, false, two-faced, double-crossing, deceitful; poetic/literary perfidious.
loyal.