Pathfinder: Kingmaker actually goes out of its way to address this with the player in multiple ways. IE, you might end up confronted further down the road if you've been getting deeply serious with multiple characters (not just from a friendship counter, but after making you've been making a number of clear and explicit dialogue choices).

One or two characters, iirc, openly allow for open relationships, but the writing makes it clear that they want to be sure there'[s some open communication going on and that the player's being at least a little mature about it. Other characters though encourage you to make up your mind and make an honest and open decision. In general it was handled pretty damn well, almost right off the bat.

Not that the way Kingmaker handles it is entirely new, a few other RPG's have done this in a somewhat similar way in the past. Even from a basic design and programming standpoint though it sounds like BG3 totally half-assed the way they implemented it. Perhaps in a partially deliberate way.