People in relationships are often looking for exclusiveness. They want to be the only person their significant other is with, and they don't want them seeing anyone else. For many people, this is the normal way their life should run. They were raised with parents who were exclusive and see nothing wrong with this attitude. Unfortunately, one of the largest causes of break ups is that one person does not really want to be in an exclusive relationship.
For those who want an open relationship, it is best to be honest with their partner. Even if they really want to be with that person, they will always feel cheated if they cannot be with others occasionally. If they are not honest with their partner, they will eventually begin to see other people secretly. Even if they are not caught, it will harm the relationship. This is a trust issue for many people, and there are few easy ways to solve it.
One way to have an open relationship with an unsure partner is to limit the type of openness. This means both partners agree they can see others, but only certain people. This gives the reluctant partner a measure of control. An escort agency might be the solution both partners seek. Escorts are people that do not seek relationships with their clients. They are available for a certain amount of time, and when that time is up they then go home.
For a couple that is intent on pursuing this type of relationship, an independent escort might be their best choice. Independents do not work with agencies, but their clientele is limited by their choice. Going this route may give the reluctant partner even more control by being able to choose the person that will be with their significant other.