Hello and good day to everyone as someone who spent her 550 hours to game and mostly romanced shadowheart during that i wanted to share what im thinking about this subject.
First of all ive read lots of frustration here comes from how players are attracted to her. I hope what im going to say will help.

1- If you are really following monogamus route, you wont hear or know about the fetishes of Shadowheart. Ive played many times, didnt get Goblin kiss my foot, shoo others who tried to come close to me. By never upping Halsins relationship with me ( basically never talked to him except he came to camp and finding thaniel) ,he never talked about how he likes me etc. In Act 2 i brought him with me and he was even mean to Shadowheart. (Animal noises banter). I will talk about drow scene after that.

2- I write this because mostly monogamus players critisized the choice here. Excuse me, what are you doing in brothel with your love interest if you are monogamus? You only go there to complete quests. Drows are not meant for you. You saw the opportunity and got punished by Halsin scene and now your feelings hurt? Again im telling this for monogamus users.

3-Youll know about Shadowhearts dream and fantasies when you share her with drows, youll learn who actually saw in her dream if you do it with Halsin. Ive played a tiefling lady, shadowheart actually let me have halsin first by her kindness. So i awarded her genereousity by letting her use my boytoy in brothel while i watch. That beach banter of Halsin made me smile even since we both enjoyed our times with him. Even though he likes me more and SH is not happy hes kisisng me like that xD

4- Halsin is not a threat to both kind of relationship. Going to drows will open poly way. So Halsins ai thinks its a Poly way with him because only poly relationship in the game with Shadowheart or Astarion.

5- Halsins beach banter with monogamus run should be a bug just like followers talk to wyll about being devil before he actually turns one. Or Gale talking about what to do in baldurs gate while in act 3 (It should happen in act 1). If not thats just another banter i wouldnt take it serious. That guy couldnt defend his grove and got caught by Goblins. It was me who saved them. He needs to be jelaous of me not other way arround.

6- About you get 2 disapproval from them is about how game thinks you are on poly way so it triggered Halsin into it. By that scene youre basically leading them on. And by refusing it turning them cold at the last moment. Ofc theyd disapprove :p

7- And lastly youll know mildly about Shadowhearts desires on good route. She showed interest to larger people like Karlach and Halsin, she says she has weakness for confident people but they usually disappoint her at the end. She also likes witty people. On monogamus you wont even know about her dreams as it should be. She wont talk to you about what she she in her dreams etc. Let the girl dream. We could be seeing a dream about riding Karlach to sunset and wake up and contunie our romance with Shadowheart.
Thats what im going to say. No need to be upset about anything.