I think that's your problem here. You're talking about something that's the norm and expecting people outside the norm to sympathise with you and be understanding and stuff. It's like a straight person going to a gay support group and saying "I had a dream that I kissed a same sex person, I'm like you guys".
That just annoys people because it feels like you're trying to be special when you're just like most people. So it's like, why don't you discuss it with anyone else, who is just like you unless they happen to be in the minority? Why is it even worth bringing up? I've never felt I had to talk to gay people about the struggle of being straight but not "absolute straight" that is disgusted by the same sex and never has same-sex dreams ever, or with black people about being a white person but not "absolute white" with no minority whatsoever in my ancestors, ever.
People are upset because after managing to decode what you meant, we've realised it is "I'm a normal person! Woe is me! Can I use the words you guy use, too? I don't want to use the same word as everybody else. I want people to think I'm special."
That's what's annoying to us. To me at least. You're perfectly allowed to be mono and aren't the only one on this forum. And there are struggles that go with being mono, I'm sure, especially in a relationship with a poly. But here you're going around saying you're poly because you aren't that thing you yourself state doesn't exist. So what's your point then? Instead of figuring that people use that word for what is the norm, must you decide it means something else, which is so rare it is some sort of oddity? Haven't you thought that the reaosn there isn't a simpler word for it that the phrase "lifelong monogamy" is that it's not happening often enough to deserve its own word, and that "lifelong monogamy" is self-explanatory specifically because everyone knows what monogamy is, and can imagine the concept of it being over your whole life rather than at one time?