Dreaming of committing adultery is an expression of repressed subconscious sexual desires considered indecent.
It might be an indication that you need to express your impulses more often and let yourself enjoy your fantasies within the limits of your established relationship with your partner.
If you dream about cheating with someone you know, it might mean that you are attracted to that person but you have subconsciously repressed this feeling because you are in a relationship.
When dreaming of your partner committing adultery, it might indicate fears, self low esteem, and weaknesses in your relationship.
Take some time, examine the reasons for your insecurity and try to trust in yourself and in your endless potential and richness as a human being.