I think they made this very intentional. Lae'zel the 'easiest' companion, it's in fact the one that is more loyal/respectful to the player. Meanwhile, Shadowheart the 'hardest to get is... well, you have seen the interaction yourself.
That and the Mizora situations are the only times she strays from her romance story otherwise. It's still worth finishing really, just don't bring Halsin into your party, go to the drows or cheat on her. It may lack a bit in content in act 3 but all of them do, it's wholesome regardless.
Originally Posted by NeedaUserName
Either we like it or not SH approves (probably likes and had participated before) orgies. Player should know this beforehand. And for the love of God, don't make her salivate for Halsin, it looks that she's more attracted to him than Tav (though some people get mad it you say so, it seems).
The only time that's hinted at is in the only two scenarios that don't make sense. She doesn't ever claim sleeping around casually was the norm and encouraged in the Sharran cloister except if you sleep with Mizora, and we know she doesn't act in character if you sleep with Mizora so anything written there is just written to make these two inconsistencies (Halsin/Mizora) make more sense.
If she was into casual sex and orgies, she should've been written as such. Any attempt to get her to do anything in act 1 or 2 is rebuked with her saying she'll take her chances waiting. She's even embarrassed about her attraction to you if you read her mind in act 1, allowing you to give a more wholesome reply than just "lets have sex lol". And all of this is despite it making most sense during act 1, because you're in a life or death situation (death by combat or ceremorphosis both being a serious threat) and her still being fully devoted to Shar and thus devoted to the teachings, including the casual sex part.
However, even if that were true (it is hinted at during some Gale/Shadowheart banter in act 1 that she prefers one night stands, which is consistent with her dialogue if you kill the Nightsong, though it's evident it's not encouraged but if anything looked down upon by Shar), it still wouldn't make sense she never acts upon it until the point where she no longer believes in Shar but believes in you instead. It should've happened in act 1 then. But that's not how she's written, therefore the act 3 scenarios are inconsistent, even with the rest of her act 3 romance.
Originally Posted by NeedaUserName
And it's funny because if there's a companion you wouldn't want this to happen is Shadowheart, you know, the trickery domain cleric, it can easily be seem as if she was manipulating Tav (though, again, some people might get mad if you say so).
As Dark Urge she claims you were the one who convinced her to spare the Nightsong. This means that you convinced her to betray Shar, the goddess that set her upon a path of lying and manipulating in the first place. If she were ever doing it, the jig is up at that point, and she's fully devoted to you, trusting that you can lead her to a better future than Shar, a literal goddess, could. This remains consistent throughout act 3, where she remains fully devoted to you all the way to the end. She even stays with you if you're a mindflayer. All this love, trust and devotion she gives you makes her claim that she wasn't surprised you'd cheat on her with Mizora complete nonsense. On the one hand she says she has full faith in you, wants to start a family with you and be with you forever and suddenly, in a single scenario that strays from all the other ones, she says she expected you to cheat on her. And it makes her not just being okay with, but actively wanting to share you make no sense either, because the only time that would logically happen would be in act 1 and 2, where she is still devoted to Shar, if they want to keep that narrative. But she isn't, she's against it then already.
