Couples in a long term relationship spend a great deal of time alone with each other. When one of them is controlling, it can be a big advantage. They may spend time subtly letting their partner know that their loved ones are less than invested in them having a good life. This is the beginning of the end because eventually the partner being controlled can begin pushing loved ones away. They may not realize what they are doing, but the end result is being isolated with their controlling partner.
The push may begin as a slight disagreement with a sibling, parent, or a child. The person being controlled has listened to their partner about a particular subject, and they believe their loved one is less than intelligent. The arguments have already been supplied by the controller, and they are often detailed specifically against a particular person. It is a formula that works well over time.
Loved ones are often quite concerned about a person, but their hurt feelings could be a distraction from recognizing that person is being controlled. They may not be willing to contact them or spend time with them as they perceive they are being suddenly treated with less respect. This works into the plans of the controller for isolating their partner, and it can be a steady separation until the final push breaks apart the family relationship between two people.
Controlling a partner is about having them listen only to their spouse, so finding ways to create a rift with their loved ones is often an imperative. The goal is to ensure the person they are controlling is the one to push others away so they can be blamed for their own isolation. It takes time and effort, but the controller is more than willing to invest in what they know will work well for them.