If you love someone - truly - love someone, you wouldn,t. And vice versa. If you did it because you felt your feelings for your other diminishing, then just tell them about it. Be open with them for christ,s sake. The fact that it had happened in the first place simply goes to show that they,re unfaithful, and either pathetic sub-human lust-machines, or simply don,t {honestly} love you. If you,re cheated on, my advice as one who,s suffered through this several times, is to walk away. They aren,t worth the agony and the time it will take to mend that fresh, bleeding wound in your heart. It will end you in the long run.