I hate it when ROs hook up with other ROs or NPCs. Like @Jender, I tend to have different runs in a game, with different NPCs that end up fitting with certain ROs, so the last thing I want to see when I’m playing one RO’s path is the RO for another character hooking up/falling in love with someone else.
As much as it adds “depth” (I would argue that that’s not really the case or necessary for NPC depth, but whatever), it also gives the reader the impression that there is a preferred coupling/tripling/whatevering and that the MC is just some tagalong that ruined a true romance when they hook up with said RO. When I play these games, I create MCs for them and then roleplay them on my playthrough–but the other MCs for that world are also in my head and they get morose when they realize they aren’t the “one” for that RO and it makes me, as a reader, feel like I’ve screwed up what was meant to be with my obtrusive MC. In short, it pisses all over my parade.
I think part of the issue is that I’m one of those people who love the whole soulmate idea, especially in fiction, so I want to see that in the IF.
When I do see this kind of thing, I pick the most appealing RO’s path and create my MC geared for that one and don’t bother with any other path, which means I mostly like will not replay the game at all, so if I know this ahead of time, I’m not buying the game–I like replayability.
I do think that, if author’s go the route of having all the ROs fall in love with someone else if the MC doesn’t hook up with them, then I think they should put a big fat warning label on it so players know what they’re getting before they shell out money for it. That said, if they made it so that it’s a choice (“do you have a problem with ROs hooking up with someone other than the MC if the MC doesn’t end up with them?”) and adjusted the story to match that choice (i.e., any section referring to it would be skipped if the player wasn’t cool with it, much like sex scenes can be skipped for those who find them squicky), then it wouldn’t be a problem. But if there’s no way to escape it? No thanks.