Ok but imagine the golden trio as being poly
I mean I'm sorry
But imagine the fluff

Their breakfast routine is that they try to take turns making breakfast but Hermione forever and Always ends up cooking because Harry either manages to nearly blows something up, Ron gets distracted, a combination of both, or they distract each other and and up play fighting or kissing in the corner

Imagine them as seventh years sleeping in the corner of the common room together because they're about to face SOMETHING dangerous tomorrow and they just need the comfort of each other

And imagine Ron and Hermione constantly kissing Harry's scar because they know he doesn't like it

Imagine Harry trying to make diluted love potions for valentines day and he just timidly goes to snape or mcgongall like 'okay but what happens if I uh use it on TWO people'

And imagine Sirius's reaction to the relationship
Just
Way too supportive
To the point where every time they all hug or kiss each other he just gasps and you practically see his tail wagging even though he's not even Animagus form

AND TONKS
"So I heard you're all eighteen now... Guess you're two times lucky, Harry*nudge nudge*"

And Remus doesn't really have a reaction to it
Just
"Uncle Remus I just want you to know that I'm polymorous and dating my two best friends and it's completely consensual and we're very happy with the arrangement, so I hope you aprove."
"Cool"

And snape finds out in like fifth year because he finds them cuddling and kissing together in Grimauld and he makES A REFERENCE TO IT DURING CLASS WHENEVER HE CAN

"Potter, I know you're partial to have more than one of something at a time, but the recipe calls for one toad arm."

"Proffeser Snape, I had more than one question!"
"As usual, Miss Granger?"

"I thought I WASN'T supposed to put in as many bloody flies as I have freckles!"
"I'm sorry, Mister Weasly, but what exactly do you know about counting?"

When Harry's nervous he likes to play with Herminone's hair though. And she doesn't mind in the least, just don't pull on it, dear.

And they try to keep it mostly under wraps but Ron can't lie to save his life so it's just like

"You all live together? So you're like roomates?"
"*face and hair match* YES YES ROOMATES HAHA YEAH WE'RE ROOMIES YEAH ROOMIES FOR LIFE"

Also consider

Ron ranting and Harry kissing him and just going 'shut the bloody hell up'