To dream that you've committed adultery means that you could have sexual desires or be sabotaging yourself. This likely comes from the root of your subconscious mind. You could be drawn into an issue that is not within your best interest such as a legal situation.
To dream that your mate or spouse has cheated means that you have concerns about abandonment. You may sense neglect within your own relationship. You could also feel as though you're not living up to what others want from others.
To dream that you are cheating with your friend's friend means that you're probably feeling forsaken by your own self.