The behavior you described, where someone who cheats becomes paranoid that their partner is cheating, can be related to psychological factors and interpersonal dynamics. While not every case is the same, there are several possible explanations for this behavior:
Projection: In psychology, projection is a defense mechanism where a person unconsciously attributes their feelings, thoughts, or behaviors onto someone else. In this case, the person who cheats may project their guilt and fear of being cheated on onto their partner. They might believe that their partner is unfaithful as a way to rationalize their own behavior or to reduce their feelings of guilt.
Guilt and Shame: Cheating can lead to feelings of guilt and shame, and these emotions can manifest as heightened suspicion and paranoia about their partner's fidelity. Their guilt may cause them to believe that their partner is capable of the same behavior they engaged in, leading to increased jealousy and mistrust.
Fear of Retribution: Some cheaters may become paranoid about their partner's fidelity because they worry that their partner will discover their infidelity and seek revenge by cheating themselves.
Low Self-Esteem: Individuals who cheat may struggle with low self-esteem and may believe they are not worthy of loyalty or fidelity. Consequently, they may assume their partner will also be unfaithful, as they perceive themselves as undeserving of a faithful partner.
Insecurity: Cheaters may feel insecure in the relationship due to their own actions. They may believe that if they are capable of cheating, their partner is also likely to be unfaithful, leading to increased suspicion and paranoia.
Self-Sabotage: Some individuals engage in self-sabotaging behaviors, such as cheating, as a way to undermine their own happiness and relationships. The paranoia about their partner cheating could be another form of self-sabotage, where they create problems in the relationship due to their own internal struggles.
It's important to note that not everyone who cheats will exhibit this paranoid behavior, and the reasons behind this behavior can vary from person to person. Additionally, some individuals may have preexisting issues with trust and insecurity that could contribute to their behavior both before and after cheating.
If you or someone you know is experiencing this pattern of behavior, it may be helpful to seek support from a qualified mental health professional. Therapy can assist in exploring the underlying issues and help develop healthier coping mechanisms and communication skills within the relationship.