A relationship is built on a foundation of trust, and violating it is a major issue for a couple. Being in an open relationship requires the couple to define the rules of openness exactly. Each person has to trust that their partner will follow the exacting requirements necessary to keep their relationship healthy. Once a person breaks any rule, the relationship suffers. It takes time and effort to prove worthy of trust, and few people are willing to give another more than a second chance.
Jealousy often appears when a person continues to break the rules of the relationship. If their partner cannot trust them, they will believe they are being unfaithful. This may sound odd in an open relationship, but it is often the case when rules are broken. Leaving jealousy behind can only happen when two people trust each other completely. There is no room for disregarding the rules in this type of arrangement.