The last two posts, jesus.
I mean I don't like that she agrees to it either and I'd like it to be rewritten but at the same time this is optional. I went to the brothel, talked to the Drow twins, told them no thanks, and that was the end of it, Shadowheart didn't say a word. If an exclusive relationship is what you were looking for I don't know why you're trying to sleep with the Drow twins in the first place. My take on it is it's something she'll agree to because it's what her significant other wants but not something she's looking for since she never asks you to do it herself and if you want to have an exclusive, monogamous relationship together she's happy to do that.