STAR BUTTERFLY and MARCO DIAZ from STAR VS. THE FORCES OF EVIL
Justification:
"Both of them were in love with each other while also being in love with other people, and the fact that they felt genuine love for multiple people was never treated as inherently wrong by the show.
More than that, each of their other partners during the show knew and even actively supported how close they were. Marco's girlfriend Jackie gleefully held hands with both of them dancing at a concert. And particularly Star's boyfriend for part of the show Tom, who grows very close to Marco, and the show even jokingly teases shipping between them. Even after finding out that Marco kissed Star, Tom doesn't hesitate to risk his life to save Marco, and affectionately pulls them both in for a group hug after the season climax. Later Tom reveals he was a little upset, not because Marco kissed Star, but because Star didn't tell him, saying "if I kissed Marco, wouldn't you want me to tell you?"
It almost felt like the show's writers wanted to do polyamory, but knew they couldn't so they got as close as they could. Star and Marco's relationships genuinely could've worked polyamorously." - @herora-nuva
Could Polyamory Have Saved Them?
Yes
No
It would make them worse
It would make them worse (affectionate)