By Mark Ryan, BACP Accredited Psychotherapist and NCPS Accredited Relationship Therapist
People often bring the phrase 'non monogamy' into a first session as though it names one thing. It doesn't. Open relationships, polyamory, swinging, relationship anarchy, and the quieter, more private arrangements couples build without ever naming them publicly, all get folded under the same umbrella, and the differences between them matter far more than the umbrella term suggests. Some of what follows will be familiar if you already practise some form of non-monogamy. Some of it is for people who are only just wondering whether monogamy, as currently arranged, is the right shape for them. Both are welcome here.
A short, honest history
Marrying for love is a newer idea than it looks. The historian Stephanie Coontz describes how, for thousands of years, marriage was mainly about economic and political advantage, such as making alliances between families, and the idea that love should be the main reason to marry only emerged in Western Europe and America in the late eighteenth century (Coontz, 2005). She also argues that the twentieth century changed marriage again, with women's growing economic independence among the forces that reshaped it (Coontz, 2005). None of this is presented to score a point against marriage. It is a reminder that the version of monogamy most of us inherited as natural is a fairly recent social arrangement, and not a timeless default that non monogamy deviates from.
People increasingly build the relationship structure that suits them, rather than accepting the one they were handed. I see that as a continuation of a long process of change in what we expect relationships to be, and not as a break from it.
What 'non monogamy' covers
Consensual non monogamy, usually shortened to CNM, is the umbrella term researchers use for relationship structures where everyone involved has agreed, knowingly and honestly, to more than one romantic or sexual connection (Gupta et al., 2024). It is worth separating this clearly from cheating, which involves no such agreement. The word doing the real work in CNM is consensual, and not non monogamous. Underneath that umbrella sit several distinct structures, and I find couples do better once they stop treating them as interchangeable.
Open relationships typically involve a primary couple who agree that one or both may have sex outside the relationship, usually without romantic attachment forming as part of the arrangement. Polyamory goes further, explicitly making room for additional loving, committed relationships alongside the original one, sometimes arranged hierarchically around a primary partnership and sometimes deliberately non-hierarchical, with no relationship ranked above another. Swinging typically centres on shared sexual experiences, often with both partners present. Relationship anarchy rejects the idea of a hierarchy of relationship types altogether, treating friendships, romantic partnerships, and everything between as worthy of the same care and negotiation rather than automatically subordinate to a 'main' relationship. None of these is a stepping stone to the others, and none is more legitimate than the rest. They are different answers to the same underlying question of how people want to structure love, sex, and commitment.
Monogamy is a choice too
One assumption sits underneath most of this conversation, and it deserves saying directly: monogamy is a relationship structure, not the default that other structures deviate from. For a great many couples, monogamy was never actively discussed, chosen, or agreed to. It was simply assumed, because it is the arrangement built into most inherited scripts about what a relationship is meant to look like. Treating it as the safe, unremarkable option, while any other structure is the one that has to justify itself, gets this backwards. Researchers have made a similar point about their own field, arguing that the premise that monogamy is the exemplary form of partnership underlies much theory and research on relationship quality (Conley et al., 2017).
Monogamy is not as airtight as its reputation suggests either, and how often infidelity is reported depends on how people are asked. In a national survey of 4,884 married women in the United States, the annual prevalence of sexual infidelity was 1.08 per cent when the question was asked in a face-to-face interview, and 6.13 per cent when women answered by computer (Whisman & Snyder, 2007). That is one study of one group, so it cannot tell us how common infidelity is in general. It does suggest that what people say aloud and what they will say privately can differ. In my work I meet relationships that consider themselves monogamous but are in practice functioning as non-consensually non monogamous: sex or emotional connection happening outside the relationship without the other partner's knowledge or agreement. None of this is an argument against monogamy, which remains a completely legitimate and often excellent choice. It is an argument against treating monogamy as though it doesn't require the same honesty, and the same active choosing, that any other relationship structure does.
What I see when couples are considering opening up
Couples rarely arrive at this decision from a position of total calm, and I want to say plainly that this is normal rather than a warning sign. Someone has usually been carrying a want, sometimes for years, before finally naming it: a fantasy about non monogamy, a friendship that has started to feel like more, a simple curiosity about whether monogamy was ever actually chosen or just assumed. The other partner is often somewhere between curious and frightened, sometimes both in the same conversation. What I find myself doing most in this early stage is slowing the couple down before any agreement gets made, because the agreements that hold up are the ones built on real clarity about what each partner wants, and not agreements built to manage one partner's anxiety or satisfy the other's urgency.
One honest pattern: couples sometimes open up in the hope that it will fix something already wrong in the relationship, a dwindling sex life, a sense of distance, boredom that has crept in unnoticed. In my experience, non-monogamy can be a wonderful choice for a relationship that is already fundamentally secure, but it rarely repairs one that isn't, and it tends to magnify whatever was already fragile rather than resolve it. Part of my work with couples at this stage is helping them tell the difference between opening up towards something they both genuinely want and opening up away from a problem they haven't yet named.
Consensual non-monogamy (CNM) is an umbrella term that covers a range of relationship styles
What the research shows
There is a persistent assumption, inside and outside therapy rooms, that non monogamous relationships must be less stable, less satisfying, or less psychologically healthy than monogamous ones. The research I can point to does not support that assumption. In a study designed to compare relationship quality, Conley and colleagues found few differences in relationship functioning between people in monogamous relationships and people in CNM relationships (Conley et al., 2017). Research on CNM is also growing quickly. A scoping review of 209 studies on polyamory and CNM found research on the outcomes of CNM relationships, attitudes towards them, how people come to them, how they work in practice, identity, families and parenting, and politics, and noted gaps still to be filled (Gupta et al., 2024). Much of this work is recent, and I would be cautious about drawing firm conclusions from any single study.
What I can say with more confidence is that stigma matters. In a study of 383 people in CNM relationships, experienced stigma was associated with psychological distress, and this link was partly explained by the stigma people anticipated and by the stigma they had absorbed themselves (Mahar et al., 2024). In another study of 339 people in CNM relationships, personal discomfort with CNM, such as wanting to change one's relationship style or feeling that CNM is unnatural, was associated with lower satisfaction with relationship agreements, lower relationship satisfaction overall and lower commitment, though not lower sexual satisfaction (Moors et al., 2021).
That matters clinically. These studies show associations, and not proof of cause, but they fit what I see. Much of the distress I meet in CNM clients is connected to the world's reaction to the relationship, and to having taken in some of that reaction before ever walking into a therapy room.
Why having an affirming therapist matters
In a study of 249 people in CNM relationships in the United States and Canada, how clients perceived their therapist's practice mattered. Clients' perceptions of affirming practices and of biased or inadequate practices predicted how helpful they found the therapy, and whether they ended it early. The clients' own comments pointed to the importance of therapists having knowledge about CNM and using affirming, non-judgemental practices (Schechinger et al., 2018). The authors concluded that therapists are positioned either to combat or to add to the minority stress that people in CNM relationships face.
An affirming therapist doesn't need to personally understand the appeal of non monogamy any more than a good doctor needs to share a patient's diet. What is required is the discipline to treat your relationship structure as a fact to be understood rather than a symptom to be corrected, and to bring the same curiosity to a polycule that I would bring to any couple.
Where jealousy fits into all of this
Jealousy comes up in nearly every conversation I have about non monogamy, understandably, and it deserves more room than a paragraph here can give it. I've written about it at greater length elsewhere: what jealousy actually is and how it behaves generally, in Why Am I So Jealous?; the particular experience of living alongside a jealous partner, in Why Is My Partner So Jealous?; and the patterns specific to non-monogamous relationships, including the difference between compersion and its absence, and what happens when one partner wants sex without love while the other wants love too, in jealousy in non monogamous relationships. If jealousy is the reason you're reading this, those three pieces will serve you better than anything I could add in summary.
Structure, agreements, and what tends to work
In my experience, couples who build lasting non monogamous arrangements tend to share a few habits rather than a particular structure. They revisit their agreements deliberately rather than assuming an early conversation still holds a year later. Needs and boundaries shift, and treating an agreement as permanent because it was once agreed is a common source of quiet resentment. They also tend to be specific rather than aspirational. 'We'll figure it out as we go' sounds flexible but often means neither partner has said what they need, whereas naming concrete boundaries, however unglamorous, gives both people something to hold onto when a difficult moment arrives.
Hierarchy deserves honesty too. In two samples (225 and 360 people), those who practised hierarchical polyamory reported lower overall relationship satisfaction and attachment security than those in non-hierarchical relationships. Participants reported lower satisfaction and attachment security with secondary and tertiary partners than with primary partners or partners in non-hierarchical relationships. The authors suggest these differences may fade with time and note that more research is needed to know whether they match what people in hierarchical relationships actually want (Flicker et al., 2021). I read this as a reason to be honest that hierarchy can carry a real cost for whoever holds the lower position, and not to assume goodwill alone will absorb it.
None of this is about finding the one correct way to do non monogamy, because there isn't one. It's about being specific enough with each other that the relationship you've agreed to is the relationship you're both living.
Where therapy fits
I work with couples, polycules, and individuals across the full range of relationship structures, and I don't come to that work trying to move anyone towards monogamy or away from it. Some of the couples I see are considering opening up for the first time and want a space to think it through honestly before making any changes. Others have been practising CNM for years and are working through something specific, jealousy, a hierarchy that no longer feels fair, an agreement that needs renegotiating, rather than the structure itself. Both are ordinary reasons to come to therapy, and neither requires you to justify your relationship shape before we get to the actual work.
If you'd like to talk any of this through, I offer a free 30-minute consultation, in person in London or by video.
About the Author
Mark Ryan is a BACP Accredited Psychotherapist and NCPS Accredited Relationship Therapist working in person across central London, from rooms in Pimlico, Kensington, and Angel. He works with couples, individuals, and polycules on relationship issues including jealousy, affairs and betrayals, sex problems, and considered separation. His practice is integrative, sex-positive, and affirming of all relationship structures and identities.
References
Conley, T. D., Matsick, J. L., Moors, A. C., & Ziegler, A. (2017). Investigation of consensually nonmonogamous relationships: Theories, methods, and new directions. Perspectives on Psychological Science, 12(2), 205 to 232.
Coontz, S. (2005). Marriage, a history: From obedience to intimacy, or how love conquered marriage. Viking.
Flicker, S. M., Sancier Barbosa, F., Moors, A. C., & Browne, L. (2021). A closer look at relationship structures: Relationship satisfaction and attachment among people who practice hierarchical and non hierarchical polyamory. Archives of Sexual Behavior, 50(4), 1401 to 1417.
Gupta, S., Tarantino, M., & Sanner, C. (2024). A scoping review of research on polyamory and consensual non monogamy: Implications for a more inclusive family science. Journal of Family Theory & Review, 16(2), 151 to 190.
Mahar, E. A., Irving, L. H., Derovanesian, A., Masterson, A., & Webster, G. D. (2024). Stigma toward consensual non monogamy: Thematic analysis and minority stress. Personality and Social Psychology Bulletin, 50(4), 571 to 586.
Moors, A. C., Schechinger, H. A., Balzarini, R., & Flicker, S. (2021). Internalized consensual non monogamy negativity and relationship quality among people engaged in polyamory, swinging, and open relationships. Archives of Sexual Behavior, 50(4), 1389 to 1400.
Schechinger, H. A., Sakaluk, J. K., & Moors, A. C. (2018). Harmful and helpful therapy practices with consensually non monogamous clients: Toward an inclusive framework. Journal of Consulting and Clinical Psychology, 86(11), 879 to 891.
Whisman, M. A., & Snyder, D. K. (2007). Sexual infidelity in a national survey of American women: Differences in prevalence and correlates as a function of method of assessment. Journal of Family Psychology, 21(2), 147 to 154.
