Thank you guys for your input, but this is exactly the kind of debate I want to avoid in this topic. This topic is not about the other companions' romantic preferences pertaining monogamy and/or poly romances, or what people view as character inconsistencies for your established romantic partners, etc. This topic is purely about Halsin's romance flags being all over the place, as people have seen with the OIO mod and which dialogue lines count as flirting. And specifically in act 3 how there seems to be a flag that doesn't properly get set when you reject Halsin in act 3, because in every following encounter he will ignore your rejection and still try to have sex with you, or with you and your current romantic partner. That's all. This is purely about Halsin' dialogue flags being a mess for over a year when it comes to romance stuff and player consent or rejection in act 3 specifically.
There are plenty of other places to discuss whether or not people feel like Astarion and Shadowheart should be poly or not, whether or not people view the consent of romantic partners well implemented with the drow twins, etc... If you want to continue that debate, please do that somewhere else.
And as I've also stated in my original post, if Halsin interpreting many innocuous dialogue lines as flirting is intentional, if Halsin coming on to you many times in act 2 without you being able to shut him down when he does so is intentional, if him being head over heels in act 3 after zero non-quest interaction and acting like you came onto him is intentional, if Halsin not taking rejection of consent and continuing to pursue having sex with you is intentional... then make that clear in a news update of sorts. As it stands, these Halsin romance interactions that seem to be very bugged to me are still in the game for over a year now. This has led to many many toxic debates and I cannot find any official statement from Larian that these Halsin interactions as they are currently in the game are 100% intentional. So I'm just requesting either a hotfix with Halsin's romance flags being properly fixed if this was not intentional, or an official news update that Halsin's romance flags are not bugged and in fact intentional so that these debates can all stop.