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.
Dream dictionary: my partner cheated on me dream meanings
To dream that you (or your partner) have a lover, suggests the unconscious desire to end your current relationship. On the other hand you feel neglected in the relationship. To dream that you are the lover indicates a desire to have an affair. Seeing a lover in the dream suggests that you are being cheated.