 " Unfaithful " is a pop and R & B ballad that runs for three minutes and forty @-@ six seconds . Originally , it was a dark and moody track inspired by the work of the American rock band Evanescence , with the initial title of " Murderer " . Hermansen and Eriksen collaborated on the melody of " Unfaithful " . In the beginning , the song 's structure was built around piano as the only instrument ; the percussion and strings was added later . The strings on the track were arranged by Robert <unk> . 
