The issue I have with the Halsin, SH and Astarion is how different it is if you romance Halsin only but neither of them. According to several ppl in the Halsin forum, Halsin shows no interest in SH or Astarion, nor they with him. But as soon you romance SH or Astarion, Halsin is suddenly interested in them, and they with him.
It makes zero sense. Why can't I just simply romance SH without the forced Halsin stuff? Like she doesn't care about him at all unless you are dating her. It is beyond bizarre.
That means she would have no interest flirting or having an orgy with him by herself. It's only when we're involved she wants this apparently...
None of the other companion romances come with this baggage. Which is unfair to those of us who wanna date SH or Astarion only. There's no reason they need to come packaged with Halsin.
So one can solo romance Halsin, but one can't solo romance SH or Astarion. How convenient.