ignoring the halsin stuff ( the one party banter line and what she says in the 5some) which is obviously some writers pet shit and completely out of character assuming she is romanced, nothing is said by the party member about sharing when talking to the drow unless you actually accept the proposal brought up by the drow twins, only after that does anyone including halsin speak.
As for why shadowheart would agree, potionbeans interpretation works best and very much is in line with her character, also she spent her whole life trying to appease shar and mother superior she will do the same for tav, its why she doesnt dump your ass for cheating but says to ask her in advance and mentions past experiences(to make it even and possiblly stir you up) or declares her non jealousy(she is) all in a disapproving tone while putting on a strong front. Though, reading reddit it seems people actually think she was fine with you sleeping with mizora and cant read tones, lots of annoyed gfs if they have any... You are possibly the only loved one in her life, she would rather share you than face the possibility of losing you over a fling or foursome(ok she was kinda enthusiastic about this one but girls can have fantasies as well, but its up to you if it stays one and its not like we wouldnt jump on a ffm threesome/ fffm foursome if she propositioned us about one).
She will gladly break up with you though before nightsong cause she is still split between you and shar.
Last edited by Neion4ty7; 13/09/2306:32 AM. Reason: fixed some typos and added text