Im convinced this is how Halsin "relationship" all of them see. This way at least it's not out of character for them. Still the point about banter as valid as ever and so is drow-twins encounter.
No reason to assume it with Halsin and not assume it with any other companions. Especially since you have to ignore a lot of implications to reach that conclusion (them calling Halsin poly, the dialogues regarding an open relationship with other companions, especially Wyll, indicating she'd not even be open to sharing once).
