Poly fidelity is a relationship structure in which three or more people commit to one another exclusively, agreeing that all romantic and sexual involvement stays within the group. It keeps the openness of polyamory in terms of how many people are in the relationship, while closing the outer boundary so no new partners are added.
People often choose it when they want multiple loving relationships but not the constant negotiation of outside dating, or when the group wants a stable shared life with all the responsibilities that come with it, like living together, raising kids, or pooling finances. In practice it usually looks like a closed polycule where everyone agrees on who is in, and everyone has to be on board before the circle changes.
Worth knowing: Everyone in the group needs to agree clearly on the rules for exclusivity and on what happens if someone wants to open things up or leave, since a closed structure can make one person feel trapped if the agreement is never revisited.
Also called: closed polycule, closed polyamory, group marriage, polyexclusivity, triad fidelity, quad fidelity, family-style polyamory, exclusive V or N arrangement
