When does SH ask the player if Karlach is someone to be threatened by? Does she ever ask how serious you are with any of the other companions? Why is she just assuming she wouldn't be the primary partner with Karlach or the others? The player should decide who is a primary partner or not, not an npc just assuming things. If SH is fine with Halsin, there's no reason she shouldn't be with Karlach, period.
I don't think the Karlach bit is well written. In fact don't think Karlach is a very well written character at all. (I know that is a very unpopular opinion)
But the only answer I can give is the one you must also give: it isn't there in the text. SH never says "nesting partner" neither does she say "exclusive", "monogamous" or any other words that would support your interpretation.
But my interpretation is consistent with all of her dialogues while yours is not. And, again, that's what you are asking for, right? To have your interpretation become cannon and my interpretation to be eliminated from the game?
