To dream that you are the one who is cheating on your partner means that you are feeling angry for something he did or didnt do, therefore the subconscious mind of yours is sending you a message that you wish for the revenge. Sometimes it simply is the fantasy which you have and means absolutely nothing. Sometimes the dream shows that you feel unhappy in small domestic things with your partner therefore you dream about cheating. If your partner is the one who is cheating on you, it could mean that you are afraid of losing him and the fact that he might find someone better than you. You do not trust yourself and think there are better partners out there. Sometimes it indicates your fear of being cheated because you are very jealous person and do not want to share your loved one with others.
Read more about dreaming of Cheating (in a relationship) in other dream meanings interpretations.