Why not? Because I would rather see a different story that's why. Other people hope this story goes down like poly relations and such and that is fine, all the power to them. I like annngst and jealousy and want to see a Mai that realized her own cowardness nearly lost her a shot at her childhood romance (which she still thinks about for because she's staring at a pic of Asumi when Sayaka walks in) and see her have to struggle for her happy ending, I'll root for her. Usually in these types of win the heart of your prostitute love interest it's characters like Asumi who has to go through the jealously and put in the work but I love a good reversal.
You say that is messed up, big deal, so is everyone who ever enjoyed a horror movie. I like stories with emotional turmoil and am not going to apologize for it. It's why I like Madoka more than Sailor Moon, doesn't man I still don't enjoy Sailor Moon btw, just like Madoka more. If this turns out to be a bubbly poly romp with no jealously and toxicity that is fine, I'll even still like it but I hope it gets a bit dark.
Hey, that's totally fine. You're admitting those themes are a "thing" for you (fetish, however you prefer to call it) and not a universal truth, and that's cool. There's just too many people around here who get like, genuinely angry when characters aren't "pure" and god forbid date or have sex with more than one person or fuck up or have messy relationships or do anything relatably human, and want bad things to happen to them because of it. IMO that's messed up (and not where you're at, I get it now).
Worse, I think it's detrimental to those people (who I am making the assumption have no or limited experience with dating and relationships) and their ability to navigate future relationships to be fixated on the "pure" romance fantasy stereotype. If you think the shining example of love is "found my one true love in middle/high school and never so much as looked at anyone else" you're in for a lot of confusion, hurt, and disappointment when you find out reality doesn't work that way.
But again, if you're self-aware enough to recognize the difference between something that appeals to you personally and a standard everyone must meet, it's all good. I have plenty of my own!