Two Faced" is 'someone who tells one group of people or an individual one thing and another group of people or an individual another thing.' You can refer to a cheater as two-faced. This is because the cheater shows one face to you-- the sweet trusting face. But there is another face you don't see-- the lying, sneaky face.
A two-faced individual: Jeff is a two-faced liar! I hate him! He told me he loved me, and then he told all his friends that I was a loser.
by Aamilah December 15, 2014