Thank you for making this topic. It's been hotly debated before and a lot of things can boil down to preferences, interpretation and visions on character consistency. One thing I personally find a glaring issue is that in some situations it ignores your Tav's consent, or even worse, pressures you and coerces Tav to consent to something after you've said no before already.
A little over a year ago, @Michieltjuhh already put the sequence of events down that can happen chronologically, so I'll link his original post and put a rewrite of that below (
original post on ignoring player character's consent):
As it is now, this is what currently happens chronologically in act 3 between Tav, a romanced Selune Shadowheart and Halsin:
1. Tav goes skinny dipping with Shadowheart and then they "make sand castles", talk about it the next day and cement the relationship between them. From here on, following through with her personal quest and finishing the game, you'll either end up together adventuring, or you'll live together in a cottage. A happily ever after together.
2. Halsin confesses his love/attraction towards your Tav in camp. You can tell Halsin you are not attracted to him. As another option you can say you are already in a relationship and then follow up that you don't want to change anything about your relationship. He says he understands your choice and when you mention your established relationship he emphasizes the importance of consent.
Here are the dialogue choices written out:
Halsin: I never quite realised how burdened I was, until I met you. The threat of the shadow curse, the politics of the grove...
Halsin: ...I forgot who I was, but you lifted the fog. Thank you.
Tav: So the fog's lifted - what have you discovered?
Halsin: You. I discovered you. I have lived a very long time. I have taken many lovers. My heart does not stir lightly. But it does now.
Tav: What are you saying exactly?
Halsin: I want more than to fight at your side, or sit around the campfire with you. I want to lay with you under the stars and feel your skin against mine.
Halsin: I think you feel the same way - why else would you have been so concerned about whether I had a lover before?
Halsin: But tell me I'm wrong, and the matter can rest. I do not wish to sour our friendship, but I have to know if it can be something more.
Tav: If I wanted to rut with half a tonne of dumb muscle, I'd seduce a deep roth�.
Halsin: A simple 'no' would have sufficed. I will trouble you with the matter no more.
OR
Tav: I'm afraid I just don't see you that way.
Halsin: I understand, and I still cherish our relationship.
Halsin: Still... I could not have forgiven myself had I not taken the plunge. Better to have tried and failed.
OR
Tav: I'd be lying if I said I wasn't interested - but I'm already in a relationship.
Halsin: You have bonded with Shadowheart, body and soul. Her scent lingers on your skin. If there is to be anything between us, it must be with her consent. And perhaps some day, her participation.
Tav: I'm sorry - I'm in a relationship. I don't want to jeopardise it.
Halsin: I understand, and I still cherish our relationship.
Halsin: Still... I could not have forgiven myself had I not taken the plunge. Better to have tried and failed.
So here you have explicitly stated you do not want to be involved with Halsin romantically/sexually or that you do not want him or someone else involved in your relationship with Shadowheart. So you either decline his advances specifically or you explicitally state you see your relationship with Shadowheart as monogamous (or at least not involving him).
3. The next time you have both Halsin and Shadowheart in your party, they will have a banter where he tries to invite himself to the next time you and Shadowheart go skinny dipping and "make sand castles". Halsin ignores that your Tav did not give consent to this just before and even explicitly stated you do not want him to involve himself. For whatever weird reason, instead of shutting Halsin down, Shadowheart says "maybe". With Shadowheart's "maybe", she is also disregarding your Tav's opinion on wanting nothing to do with Halsin romantically/sexually. As it's party banter while exploring, there is no way to interject or to speak with either of them about it afterwards to give your consent or decline this offer.
Here's the dialogue written out:
Halsin: I heard you learnt how to swim, Shadowheart - well done.
Halsin: You know, if you and your love ever wish to enjoy the waters with me, I could attempt a kelpie... or even a porpoise.
Shadowheart: Depends, are you buoyant? I may need a life preserver if I get in over my head.
4. When you visit the Drow Twins and they suggest a foursome with Shadowheart and your Tav, she says she's interested if you are, then you can agree to do it or not. Genuinely great way to approach the subject in my opinion, she gives her opinion and leaves consent entirely with Tav at this point. However, if Halsin is in the party, after you agree to a foursome with the Drow twins, he will then try to invite himself and make it a fivesome and Shadowheart agrees to it. If your Tav then declines, both Halsin and Shadowheart both disapprove of you not agreeing to this fivesome. Halsin has now for the second time ignored your Tav's explicit statement of not wanting to be involved with him sexually/romantically, or your explicit statement of not wanting him involved in your relationship with Shadowheart. Shadowheart left it at "maybe" during the party banter, now she agreed before you could give your consent and disapproves of you not wanting sex with Halsin after declining him twice already.
Here's the dialogue written out:
Sorn Orlith: A new face! Looking for another chapter of dirty lore for your biography?
Nym Orlith: You have but to ask, and we can grant you a moment of pleasure.
Nym Orlith: Don't be shy.
Halsin: An intriguing pair. Takes me back to my youth...
Tav: How did you end up here?
Sorn Orlith: I used to work as a courtesan back home, and my sister as an artisanal masseuse, but men are treated like dogs by the Underdark's matriarchs, so we fled.
Nym Orlith: We found surfacers crave the body of a Drow like a drug. Life is easy in our line of work.
Tav: Don't you want a change?
Nym Orlith: Perhaps once we have saved more gold another adventure will begin. We've had busier days, but life is comfortable here with Mamzell.
Tav: I'm glad you've found a place you feel safe.
Sorn Orlith: I'd have to restrain myself far more than any play-bindings do if I worked in another field. This is a place where I can be myself boundlessly.
Sorn Orlith: There are so many who come to me speaking of a fixation that no one else has ever been able to shaer with them... and never will again.
Sorn Orlith: A once in-a-lifetime moment of passion. Every day. What could be better? Don't you want to try it?
Sorn Orlith: Trust me, you don't want to miss my signature Menzoberranzan Love Trick.
Nym Orlith: And is that your partner with you? What a gorgeous couple... perhaps we could come to an agreement.
Tav: Agreement? What kind of agreement?
Nym Orlith: We want both of you, silly! At the same time.
Shadowheart: There's an idea. If you're comfortable sharing... so am I.
Tav: Great, let's do it.
Halsin: Perhaps you'd care for a little extra company...
Shadowheart: I won't pretend the thought hasn't crossed my mind once or twice... or more than that.
Tav: No, Halsin! Tame yourself!
Halsin: As you wish. I'm sure I can find berth elsewhere...
And as I said, that conversation ends with both Halsin and Shadowheart disapproving of your Tav not consenting to sex with someone you have already declined twice. After declining Halsin's advances at 2., both 3. and 4. completely ignore your lack of consent. Despite declining Halsin at 2., he tries to have sex with you and your established romantic partner Shadowheart not once, but twice. And instead of Shadowheart declining if she knows about your Tav's choice at 2. (what I imagine is something you would discuss with your partner after declining someone else's advances), or asking on your consent if she is not aware of your choice at 2., she wlll say "maybe" at 3. Then she will say yes at 4. before asking your consent to a fivesome including Halsin, despite asking for explicit consent for a foursome, and then disapprove of you not giving your consent to a fivesome including Halsin.
Regardless of anyone's opinion on polyamory, monogamy, etc., open communication and consent are pillars of any type of romantic and/or sexual relationship. As these events are chronologically now within the game, and have been for the past year at least judging by the original post I am referring to, there is a complete lack of respect for your Tav's consent concerning involving Halsin in your relationship. After him highlighting the importance of consent and you declining his advances towards you personally and towards your relationship with your romantic partner, he then proceeds to disrespect that your Tav declines consent and tries to convince you and your romantic partner to have sex with him. Not once, but twice. And while Shadowheart handles the offer for a foursome with the Drow twins fantastically, communicates openly and sees if you consent or decline, she will completely disregard open communication and consent when Halsin tries to have a fivesome and will disapprove of you not giving consent. To me, it's absurd that so many of your Tav's boundaries on open communication and consent are disregarded and you're even punished with hits to approval for standing your ground to say no to Halsin rather than saying no and him pressuring you until you say yes.
I propose a very simple hotfix to this disregard of player consent towards sexual propositions. If your Tav turns down Halsin's advances at 2., then stop 3. from happening all together and stop Halsin from including himself in 4. He says he respects your choice and emphasizes the importance of consent, so have his character be consistent. A hotfix like that will also solve the problem of Shadowheart approving of Halsin's advances without communicating with your Tav on consent and the possible inclusion of other romantic/sexual partners into the relationship. If you fix the issue like this, there will be no need for rewrites or anything complex, just a simple flag set after your decision at 2. so that 3. and 4. can never occur the way they are doing right now.