I remember the devs saying that it's just not feasible right now. I'm pretty sure they've been thinking about it, but I don't think that'll be implemented any time soon.
It might just be me, but I think dating two characters at once would require additional dialogue and significant changes in story direction, and that will take a lot more time than intended.
As ShroudedLion said, we will not be implementing poly relationships mostly because we don't want it to be... "forced". Like how shipping between characters then inserting the Scriviner in that relationship, or vice versa.
Once we get a better idea of polycules, we might implement it, but with our current experience (both irl and in media), we are not ready to even dive into the thought yet.
Especially ships that are a bit more... risque
