The term 'are unfaithful' refers to someone who is disloyal or cheats in a relationship or marriage. There are numerous synonyms that can be used to replace this phrase. For example, a person who is unfaithful can be described as being adulterous or promiscuous. Other synonyms include deceitful, treacherous, and dishonest. Infidelity, cheating, and cheating on someone are also common phrases that can be interchanged with 'are unfaithful'. Regardless of the specific term used, this behavior can cause immense pain and heartache for the partner who has been betrayed, and should be addressed with empathy and respect.