Yes, it is possible for a relationship to work when one is monogamous and the other is polyamorous. This is often called a "mono-poly relationship" or a "hybrid relationship."
However, let's be clear: it's not easy. "Mono-poly relationships" are indeed possible, but require partners who are secure in themselves and their choices, secure in the relationship, good communicators, and willing to do the work.
As I wrote elsewhere in this FAQ, polyamory is a form of consensual, or ethical, non-monogamy (ENM) in which a person is involved with multiple romantic or sexual partners at the same time. Consent is crucial. One of the most important parts of being polyamorous is making sure that you — and any romantic or sexual partners you have — are aware of and consent to the relationships you have with them and others.
All of this means that communication and consent is still the key. The polyamorous person may decide to follow any type of polyamorous lifestyle while their monogamous partner does not. And when both communication and consent are fully present, the mono-poly relationship can be a healthy one where both partners are getting their needs met.
But it's important to note these realistic caveats:
- Without communication and consent, it's cheating. If you're in a monogamous marriage and your monogamous spouse betrays your trust by sleeping with someone else outside your marriage, but says to you, "It's not cheating. I'm polyamorous," they are wrong. It is cheating, and you are absolutely entitled to feel hurt, angry, and confused. If you never consented to being in an polyamorous relationship, you have every reason to view their activity as unfaithful. There's even a term for this: polybombing.
- If the relationship started as a monogamous one and one partner starts to identify as polyamorous, it is often very hard for the one who has remained monogamous to manage that shift. Often, people who are monogamous don’t understand why a person would want to be polyamorous. This can sometimes lead to feeling that a polyamorous partner is looking to replace them or that if they just work hard enough, the polyamorous person will snap back and become monogamous with them again.
- Many couples decide to pursue polyamory as a way of "saving" their marriage or long-term relationship if there's a history of cheating and infidelity. There is one inherent flaw in this thinking: whatever is wrong with the marriage or relationship usually is not the sort of problem that can be remedied via polyamory. Indeed, polyamory will put huge stress on a relationship and exacerbate any existing flaws or problems. The pressure will cause the relationship to crack or shatter long before the couple reach a point of new stability.
In her book, The State of Affairs: Rethinking Infidelity, relationship expert and psychotherapist Ester Perel notes that people in happy relationships cheat not because they want to leave the marriage, but because they want to leave the person they’ve become.
"Consensual nonmonogamy means that both partners have equal say in the decision to take unfulfilled hankerings elsewhere," Ester says. "In contrast, infidelity is a unilateral decision, in which one person secretly negotiates the best deal for themselves."