Polyfidelity

Polyfidelity is a relationship between three or more people who are exclusive with each other and closed to anyone outside the group. The name is exact: poly for the number, fidelity for the exclusivity.

It is the arrangement that makes the clearest case that non-monogamy and faithfulness are separate questions. A polyfidelitous group is non-monogamous — more than two people — and entirely exclusive. Nobody in it is available to anyone else.

This is the entry's main job, because these four get used interchangeably and are not the same thing.

• [Polyamory](/base/polyamory) is multiple romantic relationships. It may be open to new ones or closed; polyfidelity is the closed case.
• An open relationship is a couple who are sexually non-exclusive. Polyfidelity is the opposite on that axis: exclusive, with more than two people inside the boundary.
• A [throuple](/base/throuple) is the three-person case of polyfidelity, when it is closed. An open triad exists too and is not polyfidelitous.
• [ENM](/base/ethical-non-monogamy) is the umbrella over all of it.

One useful way to hold it: monogamy draws a boundary around two people. Polyfidelity draws the same kind of boundary around three or more. The boundary is not weaker, it is just larger.

The reasons people give tend to be the same reasons people give for monogamy, which is the point.

Security. A closed group removes the standing question of who else might arrive. For anyone with an anxious attachment pattern, that question is expensive to keep open, and the closed structure answers it permanently rather than repeatedly.

Depth over breadth. Time is the binding constraint in every non-monogamous arrangement. A closed group of three or four is the largest number most people can sustain real relationships with, and closing it is an acknowledgement of that rather than a restriction.

Practicality. Shared housing, finances and children are easier to organise around a fixed set of adults. Groups raising children together move toward polyfidelity noticeably often.

Sexual health agreements. A closed group can make agreements about testing and barriers that an open one manages differently.

Closing is a decision that has to be made rather than assumed. Groups that formed out of polyamory sometimes drift into polyfidelity without naming it, which produces a disagreement later about whether a rule was ever agreed.

New members change the whole structure. Adding a fourth person to a closed three is not the same as a couple adding a partner — it is a renegotiation involving everyone, and the existing members have unequal enthusiasm for it more often than not.

An ending is more complicated than a breakup. When one relationship inside the group fails, the others do not automatically fail with it, and the group has to decide whether it is now a smaller closed group, an open one, or over. There is no script for this and it is the most-cited hard moment in the practitioner literature.

The legal position is the same as any multi-partner arrangement: essentially unrecognised, and everything has to be built from wills, powers of attorney and cohabitation agreements.