I think the only way anyone could upset me with headcanons would be if they killed off one of the trio in order to make the ship “pure”.
I had a snarky tag comment a while ago from a person I have since blocked, who was complaining in the tags that I had ruined a “pure” m/m ship by adding Ursula, and I was this close to replying to them publicly and watching them get eviscerated because excuse u, my poly queer ship is entirely pure as is, tyvm. It was always a poly queer romance right from the very inception. I didn’t just shoehorn in a female character at the last minute just for funsies and to piss people off, the plan was always to have a m/m/f poly trio who fall in love and live (that’s an important part, LIVE. I edited so much toxic poly smut back in the day where someone always died and left the “true otp” behind and I H A T E D it HAAAATED IT) happily ever after.
Which isn’t to say you couldn’t ever write fic about one or more of them dying if you wanted to (
you monster, I’m just kidding) I’m just saying that one of them dying doesn’t erase the fact that the characters are and always will be queer and don’t conform to the simplistic binary of gay or straight. They’re bi/pan and that’s perfectly “pure” enough. So I mean, you can kill Ursula off if you wanted to to make a “pure” gay ship, but uh, that’d make you a pretty terrible person, sorry. I don’t make the rules.
Actually in this instance I do. And they’re poly bi/pan queer immortal idiots in love and there’s nothing you can do about it.