Nobody has said this already so I'll bring it up. I don't think this type of interactive media can depict healthy polyamory. In a TV show or Movie absolutely, it's more like a voyeuristic experience, you're watching, detached from the actual plot on the screen.

In interactive media, especially in an RPG, you're the one making these decisions. You're practically the center of the universe, all things revolve around you and what you do, no matter how good the game is at hiding that fact, you are the center of attention. That makes for a pretty unbalanced relationship. When comparing it to a linear movie, I imagine it's way more difficult to implement poly into a video game that already has a million possible little decisions that multiply further along. Devoting so much time to managing relationship mechanics would take away from the actual game due to how complex it would become (this game isn't a dating sim after all).

Most implementations of polyamory in video games will have no real depth as a result, all it'll amount to is "the player can have multiple romantic partners at once" ignoring the nuance of a real relationship. Do you really expect Larian to do a good job of implementing things like relationship anarchy for example, given their past handling of simple flags (or lack thereof)

I'm not throwing shade at anybody here, you're free to have your opinion, this is just my take. You can have undeniably undeveloped poly or have no poly (i just don't think they will commit so MANY resources to fix what is a very niche issue, nor do I think they will actually remove it). I'm not against the idea of having polyamory in this game, as long as it has proper build-up and writing backing it up. I'm not intending to put anyone down or challenge anybody's view, if you think the content of this game is fine as is, more power to you! All i want from Larian is a farm epilogue and a bug fix for what is a simple issue that can be effortlessly fixed with proper flags, that is all I want and expect from them.