If you dream that you commit adultery or cheating on someone, this is a sign of you not being honest with yourself. Maybe there are some things in your life you can not admit to yourself and hiding the feelings deep down inside of you. Also, this could be a sign of you being invoked into something against the law. If you see your partner or your friend cheating on you, this is a sign that you are afraid of being neglected by the ones you love. You should consider, as there might be something missing in the relationships you are having, that why you are having those fears. What you should do is not humble yourself down. If you dream of cheating on your partner with his friend, this is a sign that there are changes that has to be done in your relationship with your partner, as you feel unappreciated. You might reveal something about your partner you will not like.
Read more about dreaming of Adultery in other dream meanings interpretations.