For most people and most relationships, the mainstream monogamous relationship model fits and there is no need for them to question it overmuch. The mistake is not doing what works for you if monogamy is what that is, it’s assuming that mono-to-poly relationships are the only ones where the terms of the relationship change.
I’m not just saying this because I’m poly and tired of my relationship style being treated as the only one where painfully-common problems arise (though yes, I rather am, thank you). I’m also saying this because a lot of wholly-avoidable issues come up in relationships of all kinds when people don’t acknowledge those changes for what they are.
While I know that some people swoon directly into each others’ arm at first sight and swear eternal undying devotion and commitment to one another and immediately run off to a courthouse to wed, very few monogamous married relationships start out exactly like that. The script often goes something like this: You meet someone, get to know them (a little or a lot) and assess mutual romantic/sexual interest, have a few (or many) dates before you are officially In a Serious Relationship with them, spend some time in a relationship before you decide whether or not to marry, and then either get married or restart the process with a new person.
That is more or less the mainstream heterosexual script for starting a lifelong relationship (YMMV). And guess what? That trajectory reflects several changes in the terms of a relationship along the way. You weren’t legally married to (or, if it went the other way, broken up with) them when you were in a committed non-marriage relationship with them, you weren’t in a committed relationship with them when you were in the deciding/dating phase, and you weren’t dating them when you’d just met them and/or were getting to know them. The terms of your relationship with that person changed several times and there was nothing wrong with that since you both talked about and agreed to those changes (or I’d hope so).
Because monogamy is still very much the mainstream ideal and norm for relationships, it may be hard to see shifts that follow the script as changes in the terms of a relationship, yet that’s exactly what they are. And because even positive change can create or aggravate stress, monogamous folks would do well to examine them carefully. Lots of people who truly love their partner and sincerely agreed to the change in the terms of the relationship were still challenged by, say, moving in with, getting married to, and/or having a child with that partner.
Additionally, just because a certain change in the terms of a relationship is commonly done doesn’t mean that it’s necessary for that particular relationship or person(s). Relationship advice columns are rife with questions from people worried about their relationship not progressing along what they feel is the socially-acceptable timeline. Additionally, there are people who sort of shrug and go along with typical relationship milestones because that’s what they think they ought or even have to do. Being monogamous doesn’t have to mean following that script, but sadly, a lot of people don’t realize that there are, indeed, options.
Acknowledging that all relationships are negotiated and experience many kinds of change over time may seem obvious, but it isn’t always obvious when your relationship is the mainstream kind. That’s why I can say that everything I learned about monogamy comes from being polyamorous. While I am not any sort of monogamy expert, having a relationship style that by definition cannot rely on pre-set societal norms means I have to talk about and think about my relationships more than I would if I could default to a script. All relationships could do with more self-reflection and specific, explicit conversations about their respective terms rather than reliance on a set of assumptions.