There's this thing that people who are exploring polyamory for the first time as part of a couple do, and I don't see it happen when people attempt to try polyamory as a single person. It doesn't matter if the "couple" is dating together, dating individually, unicorn hunting or not, or how long the relationship has existed prior to the poly exploration. And there's this thing that a lot of poly "veterans" keep trying to do, but a lot of poly veterans learned the hard way that it's not the most successful strategy so they don't do it anymore. The thing they do is set out trying to find additional partners "without risking or disrupting the pre-existing relationship".
Every time, these new explorations are attempted while simultaneously attempting to keep the pre-existing relationship exactly the same, only, y'know, with more people. I get it, I mean, they love each other, otherwise they'd break up and start dating someone new. Kind of the whole point of polyamory is that you get to start dating someone new without losing anyone old.
Single people, however, don't try to find a partner with the assumption that their life will look exactly the same after they get a new partner as it did before. We seem to instinctively understand that, no matter what relationship type - poly or mono - dating someone new means things will be a little different. Compromises will have to be made based on who the new person ends up being, some plans get put on the back burner, some priorities get reshuffled, some things get given up and some new things get adopted.
Sometimes we can predict which of our things will be affected, like a guy who assumes that he'll have less time for Monday Night Football once he gets a girlfriend who doesn't like it, and other things we can't predict like waking up one day and realizing that we haven't actually touched our scuba equipment in months because our new partner doesn't dive and we'd rather spend time with them.
Every once in a while, we decide that our pre-dating proclamation to never ever leave the city we're in because we love it so much, ever, no matter what, doesn't feel as strong in the face of our soulmate announcing their intention to move back to their home country. Some people who thought they'd never even consider dating someone with a kid from a previous relationship find themselves being a step-parent because their True Love just happened to come with a kid. Life ends up looking different than it did before dating, and we all just kind of know that.
But couples seem to think that they can preserve and protect their relationship from experiencing any kind of change or disruption if they just find the "right partner" or if they make a bunch of rules dictating the speed and direction the new relationships are allowed to take, to make the change happen slow enough that it's essentially unnoticeable. There's a fundamental flaw that makes this strategy inherently less likely to succeed. Only Franklin said it better than I could - I'd ramble on for pages, so I'll let him say it:
There will be disruption. You can't avoid that. Your pre-existing relationship *will change*. The only thing that trying to prevent change will do is hurt the new person, and quite likely hurt the pre-existing relationship that you were seeking to protect in the first place. Have you ever tried to put ice into a glass of water without affecting the water level? It can't be done. The presence of the new ice *affects* the existing water. And if it's the middle of winter and you have hypothermia, adding ice is probably going to be a foolish idea. But if it's the middle of summer, and it's hot, and you're sweating, and you take that ice water onto the porch where there's a bit of a breeze, to sip while reading a good book on the porch swing, well, adding that ice makes the water a whole lot better.
It's not a terrific analogy. As I said, I'll ramble on for pages, even after Franklin already said all there needed to be said on the subject. There will be change and you can't avoid it. But you might be turning your pre-existing relationship into something better, if you just let the change happen instead of trying to prevent it.
See also: https://joreth.dreamwidth.org/376186.html - The Most Skipped Step[s] When "Opening A Relationship" + 1
Every time, these new explorations are attempted while simultaneously attempting to keep the pre-existing relationship exactly the same, only, y'know, with more people. I get it, I mean, they love each other, otherwise they'd break up and start dating someone new. Kind of the whole point of polyamory is that you get to start dating someone new without losing anyone old.
Single people, however, don't try to find a partner with the assumption that their life will look exactly the same after they get a new partner as it did before. We seem to instinctively understand that, no matter what relationship type - poly or mono - dating someone new means things will be a little different. Compromises will have to be made based on who the new person ends up being, some plans get put on the back burner, some priorities get reshuffled, some things get given up and some new things get adopted.
Sometimes we can predict which of our things will be affected, like a guy who assumes that he'll have less time for Monday Night Football once he gets a girlfriend who doesn't like it, and other things we can't predict like waking up one day and realizing that we haven't actually touched our scuba equipment in months because our new partner doesn't dive and we'd rather spend time with them.
Every once in a while, we decide that our pre-dating proclamation to never ever leave the city we're in because we love it so much, ever, no matter what, doesn't feel as strong in the face of our soulmate announcing their intention to move back to their home country. Some people who thought they'd never even consider dating someone with a kid from a previous relationship find themselves being a step-parent because their True Love just happened to come with a kid. Life ends up looking different than it did before dating, and we all just kind of know that.
But couples seem to think that they can preserve and protect their relationship from experiencing any kind of change or disruption if they just find the "right partner" or if they make a bunch of rules dictating the speed and direction the new relationships are allowed to take, to make the change happen slow enough that it's essentially unnoticeable. There's a fundamental flaw that makes this strategy inherently less likely to succeed. Only Franklin said it better than I could - I'd ramble on for pages, so I'll let him say it:
There is one fly in the ointment: If you introduce someone new into your life, you DO risk disruption.
A lot of otherwise decent people do many very evil things in the name of protecting their existing relationships from disruption. But disruption is a fact of life. You can't introduce someone new into your life without risking disruption, and that's okay.
Almost everything you do in your life risks disruption to your relationships. Taking a new job. Losing a job. (Couples counselors say that financial stress is more likely to ruin a relationship than any other single factor, including cheating.) Deciding to have a baby. Moving to another city. An illness or injury. Problems in the family of origin. A death in the family. New hobbies. Hell, every time you walk outside your door or step into a car, you're risking serious injury or death, and that'll disrupt a relationship real quick!
We don't live in fear of disruption when we're offered a new job or decide to have a child. We accept that these things will change our lives, and move on. Ethical polyamory is the same thing: you accept that changes in your romantic life may affect your relationship, you resolve to act with integrity and honesty to cherish your partners to the best of your ability, you trust that your partners will do the same thing, and you move on.

It's not a terrific analogy. As I said, I'll ramble on for pages, even after Franklin already said all there needed to be said on the subject. There will be change and you can't avoid it. But you might be turning your pre-existing relationship into something better, if you just let the change happen instead of trying to prevent it.
See also: https://joreth.dreamwidth.org/376186.html - The Most Skipped Step[s] When "Opening A Relationship" + 1