Guilty by Transference
A person who is innocent of cheating but accused of it will often try to figure out the source of the accusation, and they will search their memory to see if their behavior could in any way make them look unfaithful to their partner. They may have friends or relatives who have cheated in the past, and they may believe it is best to stay away from them. They do not want to be guilty by association.
Transference is when a person violates the rules of a relationship and then transfers the guilt of that action to their partner. In the case of cheating, they convince themselves that their partner has done the same thing. The other person in the relationship is guilty because the accuser believes they must be acting in the same manner, and proof is never an issue with this type of reasoning. A partner who is constantly accused without proof or reason should consider transference as the source of the accusations and consider leaving the relationship.