The PC can be freely pansexual, as its your game to be attracted to whomever and what ever you want in the game, just being more inclusive is why I said it. As for the companions, I feel it more compelling if not all the companion characters were not like that, unless their character is like that, for example Astarion, it fits his character. They should have stricter character lore on who they are. By making everyone bisexual just feels like an easy cop out, and feels cheap on the story side of the characters.
