Eh, I see zero issue with having diverging romance paths with different facial expressions for Astarion. Afraid, neutral, happy, seems fine. Like the thread this is based on, would feel most natural if tied to dialogue choices. If there has to be only one, neutral is the compromise, but I do think it would be better if there was a divergence.
And why would it be necessary to have divergent romantic paths if someone who doesn't want an eternal bond with Astarion, and who might make a miserable face because of it, "wanting freedom", can immediately say, "No" in response to Astarion's proposal and break off the relationship with him? Astarion makes it clear that it will be an eternal bond, and it's extremely odd for someone who considers it unfreedom to agree to a conversion ritual to then try to break something that can't be broken. To roleplay a character who is completely unable to predict the consequences of their actions? And someone who truly loves Astarion, who is happy that they will be together forever until the world falls down, who themselves would never let Astarion go far away from them of their own free will, why should they kiss their beloved with a neutral face?
I don't think there is a double standard, either. It's believeable for the darker Astarion pathing, but not so much for Wyll. There is one standard applied to all, and Astarion sits on top of the spectrum.
I don't see the same standard being applied to everyone. No one but those who love Astarion has been tried to be made to be miserable in the game. There was an attempt in which Minthara insulted the DU who refused to accept Bhaal, but thankfully that was quickly removed. But that incident with Minhara is the only one, nothing else like that happens to any of the romantic companions in the game.
So many points... Let's start with:
"I don't see the same standard being applied to everyone. No one but those who love Astarion has been tried to be made to be miserable in the game."
Well, there is Karlach. Larian very much made us believe for months that all our effort was for nothing, and that she is doomed to die. The Avernus ending being a "badass" route where the whole party doesn't die in 3 months or so is a rather recent invention. It's not possible to survive permanently there -- for multiple reasons! -- so this one requires immense suspension of disbelief from me to this day. Nonetheless, we got something. I can live with what we got.
It's not completely equal to what happened with Astarion, no, but as I've said -- that does not mean other companions do not have *similar* complexity. In parallel: the last time I played the game, SH was bugged into the Dark Justiciar route! I had to *kill* her since this wasn't an evil playthrough.
"And why would it be necessary to have divergent romantic paths if someone who doesn't want an eternal bond with Astarion..."
Nothing is *necessary*. In a way, I could level the same criticism at happy expressions -- the only fix "needed" is complete neutrality. However, I believe both could enrich the experience, albeit for different people.
"To roleplay a character who is completely unable to predict the consequences of their actions?"
I am a realist, so him turning more "evil" is obvious to me, but there actually were a lot of people surprised that he does and that this is the dark route when the game came out. They fundamentally disagree on it being the "dark" choice. I can see a Tav thinking in a similar style to these people -- the vampire spawn could wreck a lot of havoc, and Astarion "deserves" his freedom. Therefore, the ritual is... not inherently evil. I don't agree with this line of thinking, but yes, I could roleplay it.