This section is from the book "How To Intepret Your Dreams", by An Unknown Author.
To dream that you are cheating on your spouse, mate, fiance, or significant other suggests feelings of self-guilt and self-betrayal. You may have compromised your beliefs or integrity and/or are wasting your energy and time on fruitless endeavors.
Alternatively, it reflects the intensity of your sexual passion and exploring areas of your sexuality. It is actually a reaffirmation of your commitment. Furthermore, it is not uncommon for people approaching a wedding to have dreams about erotic experiences with partners other than their intended spouses. Most likely, such dreams represent the newness of your sexual passion. It may also signify anxieties of changing your identity - that of a spouse.
To dream that your mate, spouse, or significant other is cheating on you indicates your fears of being abandoned. You may feel a lack of attention in the relationship. Alternatively, you may feel that you are not measuring up to the expectations of others. This notion may stem from issues of trust or self-esteem. The dream could also indicate that you are unconsciously picking up hints and cues that your significant other is not being completely truth or is not fully committed in the relationship.
To dream that you are cheating at a game, suggests that you are not being honest with yourself.