Please, if you can, in your own words ....
Define what is the difference between a friendship/fuck buddy relationship and a polyamorous relationship ?
While we're at it ... you can just fill in between the lines.
DEFINE: HOOK-UP (what does that look like?):
I'm ok with sharing sex upon very short acquaintance with no relationship expectations. It is fine if I never see the person again. I might go home with someone I just met somewhere, or find someone online. Extremely casual, NSA. Also, people who are friends, but have sex once and then never again and decide that ONLY friends is better, "hooked up" once. No expectation of a repeat.
DEFINE: FUCK-BUDDY (what does THAT look like?):
"Booty call" status where there is some ongoing communication, but no relationship expectations. Example, a fling I had last year, the Worm King, if he invited me over, the expectation and pattern every single time, was we'd talk, drink tea, maybe eat, and sex would happen, and usually I'd go home though I spent the night once or twice. Sex was the point and the purpose of our interactions. We never saw one another otherwise. We had a bit of friendship (conversations) but pretty much only because we wanted to have sex with each other.
Adding a category: FRIENDS WITH BENEFITS: This category is heavier on the friendship, and the friendship is considered more important than sex, but people have one another's general sexual consent and the option is open. Can be very close and enduring friendship. However I have found that with more narrow minded folks subject to cultural assumptions, once a person who does FWB gets into a mono relationship, they drop contact with former FWB. New partner is usually uncomfortable, or would be hinge type person doesn't want new partner to feel jealous. This need not happen (in my opinion) with openminded people who trust each other, though. The benefits could drop off and the friendship continue.
DEFINE: Primary Poly Relationship ...
DEFINE: Secondary Poly Relationship ...
Assuming a person is doing hierarchy, which not all do... The Primary is the main relationship, likely a spouse or "nesting" partner (living together) subject to a greater expectation of permanence and entanglement. The Primary usually gets certain assurances that Secondaries will not threaten the Primary relationship. Sometimes there is veto power, where the Primary can tell the Hinge to stop seeing a Secondary.
The Secondary is an additional, non-Primary partner of some sort. Might be in relationships with a Primary couple (unicorn) or might be only with one of the two. Might move in and live with them, or not (solo poly.) This works best for independent solo poly types who prefer no entanglement (moving in, having kids, marriage) and want to enjoy the feeling of a relationship without the pressure of expectations to step up life commitments.
The hierarchical model with Primaries and Secondaries is often criticized as being highly unfair to Secondaries especially. (Look up terms "unicorn", "unicorn hunter" and "couple privilege.") However, I think that if people involved are clear and in agreement about desires and expectations and needs, and good at communicating so that terms can be renegotiated if necessary...there is nothing wrong with doing hierarchy, if hierarchy is right for you.
and so on with whatever else may fit in between those defined lines ...
A few other relationship structures/helpful terms:
Solo poly: Your mythical unicorn, the poly person who is willing to do multiple relationships, but chooses to live alone and doesn't seek a partner with whom to entangle life logistics, marry, have kids, etc.
Relationship Anarchy: A poly person who reserves the right to place any level of investment in any kind of relationship and who rejects the "rules" or expectations of what different roles are supposed to entail. A friend might be a partner who lives with them, a spouse might not be a sex partner, and lovers might rank lower than all...there is NO hierarchy. Levels of loyalty and commitment and emotional attachment are not related to the relationship label that a person in one's life bears. RA's kind of make it up as they go.
Egalitarian Poly: The kind of poly where participants intend and act to make all partners "equal." It can be functionally difficult to accomplish in most poly groups that start with an existing couple and open to include more.
One question that someone once said, to illustrate if one is really doing egalitarian poly or not, is:
Let's say you're married and one spouse is military or has a high earning career, and is relocated to a new place far from the original home. The other spouse in most marriages, will go along with. Kids or no kids, they'll usually relocate to be with the spouse who had to move. If there is a "third" who is theoretically supposed to be "equal" then questions like:
Would they also move with the couple?
What if they were the big earner or military and they moved, would the couple go with?
A no answer to either of these questions tends to show up a lesser degree of committed entanglement with the life of the "third" and a likelihood that they are at least partially secondary, even if they aren't treated as inferior. Which is fine. But good to be aware of.