if Helayna is in Rowan's room, but those don't come with any hits to stats as far as I'm aware. I don't think it locks off any Alexia scenes, either.
Alexia has to be in Rowan’s room for one or two RowanxAlexia scenes to activate (unless that’s changed since I last looked into them, which was quite a while ago since I nearly always end up with them in separate rooms).
The big ones would be the various outcomes for Helayna:
On top of that, there are a few others worth mentioning.
Your choices regarding Delane in the Orciad have some impact on how Rastedel plays out.
Choosing whether to move into the same room as Alexia, and subsequently choosing whether to claim Helayna, can affect access to a couple RowanxAlexia scenes (which require Alexia in Rowan’s room) as well as virtually all Helayna scenes (which require Helayna being claimed).
Making choices that leave Rowan and Alexia uncorrupted will significantly impact some of their scenes and scene access (especially Alexia, who needs to be corrupted to progress down her Jezera/Andras paths). By that some token, corrupted Alexia will have to choose between going on the Andras or Jezera path (assuming either is available), and each path blocks access to the other.
Those are off the top of my head for the choice scenarios that have significant scene access consequences in the current build (well, technically two or three builds ago), but I could be missing some. And of course this isn’t including the ones that are building to significant plot-relevant consequences since we’re still in act one and those consequences haven’t been explored fully yet.
When's the next update I've literally lost all sense of time these days
Should be end of Jan.
