I’ve voiced my feelings on this topic before, I believe. I do not like it when ROs hook up with other characters. Well, let me rephrase that–for paths I intend to play and go through the trouble of creating an MC (I don’t self insert and I don’t use the same MC for all paths), it irritates me (and whatever character I created for a path) to see the RO hooking up with someone else. Granted, it’s kind of like having AUs, but there’s something about it that still grates because it breaks reader immersion to see it happen (and leaves me feeling like I made an MC that ruins the “true” path for the RO the author intended).
I also feel that, when it’s done, not only does having a RO fall in love with someone else detract from the game and its replayability, but it also adds nothing positive. It wastes valuable narrative that could’ve otherwise been used to expand the story for the MC (perhaps friendship with that RO, or a side quest with them). I really don’t play games so I can read about a romance that has absolutely nothing to do with the MC or the MC’s journey–if I want that, I’ll go read a book. So either put more effort into the MC’s relationship with the chosen RO or into a friendship with the possible LI that wasn’t chosen. If the author is that married to getting the ROs paired off with others, then let it be a choice for the reader to help that along (or not) as a friend to the LI or don’t bother with it. Personally, I think there are better plots to have the MC and “not” RO party members pursue instead.
Alternative: let the player choose the name of the LI for the “not chosen” LI. Then they can plug their other MC’s name into it and immersion flows between playthroughs. Easy enough to do.
All that said, in the game I’ve started, one romance option is actually a poly with two people who are together but looking for the third (it’s a soulmate sitch and they aren’t human and have their own thing that’d take too long to explain). In that case, it’s either going to be the MC being the third or they never get their third onscreen/in the game.