Yes, Astarion does react to attitudes towards him, and romance with him can look a lot of different ways. I used to like it a lot (and still do, despite the fact that with those kisses the author arbitrarily tried to bend everyone to someone else's headcanon). It makes him even more alive, more like a real person. Reacting to the way he is treated. We treat different people differently too, you can adore someone and despise someone. You can start with adoration, and then find out what that person is like, and then you can start to despise them. And that adds value to the romance with Astarion. You go through your happy romance, then you get to watch Astarion react to bitchy, silly lines that you yourself completely dislike, and it's much more interesting than a "wimpy" character who succumbs to everyone regardless of their behavior. I really liked the video where Astarion rejects Tav when Tav forces him to bite Oblodra. The first part of the video is heavy as he asks: "Trading me for some potion?", how he bites that nasty drow, how he vomits afterward. I was prepared for this viewing, I knew I would see his pain, and I thought he would look betrayed, suffering in his conversation with Tav. And he sent her off so beautifully! The contempt in his voice, he realized exactly who was in front of him, he didn't believe any manipulative apology, any excuse. Not like Gale, who cries for Mystra, who betrayed him, who left him in the worst of circumstances, who feels guilty for her and continues to love her. I sympathize with Gale purely as a friend, but if a man I like as a man behaved like that, my opinion of him would clearly deteriorate.
In the case of AA in these versions, where he screams with anger and pain, I myself feel bad for him that he not only got involved with such a Tav, but also believed, as the only person close to him, that he still wants to hold on to them, that because of his great need for love he fixated this need on someone who doesn't deserve it, who he doesn't need, and can't break this relationship himself. Although in the case of the first time I didn't realize that the "No" in the kneeling scene (it was still painful to me at the time, I didn't understand anything, didn't understand what it was for, etc.) means that Tav refuses to be converted to a spawn, not that she doesn't want to be humiliated and hopes to explain something to Astarion, Astarion promises to find someone better, it's certainly hurtful. It's a stab in the heart. But in fact, Astarion himself says so because of deep resentment and pain. When you come to him in the morning, he swears, turns away and I felt like a traitor, I ended these problems with this kneeling, like, okay, you want me to kneel down, you want me to stand on my head, you want me to stand on my ears, just to avoid seeing Astarion, who is terribly offended and betrayed by me. So I myself once had a specific "failure" of an romance with him because of a misunderstanding of the situation.
It's interesting about "so-called friends", because they're not really friends-friends for me either, I treat some of them quite well, I had some responsibility while I was considered the leader of the group, but, in general, Astarion is right. Those friends would have a pretty good laugh at him if he was burning at the docks. Especially since they include Halsin, Jaheira with her promises of being an annoying neighbor, and Minsc with his Astarion-monster. From Lae, Shadowheart, Will, Carlach, Gale, who teaches at Waterdeep, I really don't expect any special setup, but I really wanted to keep an eye on Jaheira (Minsc is too dumb not to notice if he's plotting something against Astarion and me). The only thing I can call a friend is Lae'zel, I feel like she'll really come to the rescue regardless of the morality of the situation, it's like an old battle buddy. But it's better to have Astarion be a bit of a paranoid spy on everyone than to be careless and trust everyone and everything, the latter of which could end badly. I like the line where he promises to keep an eye on me, Tav then in clumsy warrior stealth tried to watch him herself the whole party (he's a pleasure to watch - he does so many interesting things!). I wonder how someone who watches your every move will react when he notices you're watching his every move?

It's fun. If such a relationship were real, friends would probably hate such a couple who only play games with each other, and they themselves would start yelling, saying, "Why did you two come here in the first place? You should stay at home if you're not interested in anything else but each other!"

But also, a real life abuser is going to abuse their partner regardless of how nice they are to them. It might put off the abuse for a bit, but there's only so much walking on eggshells you can do.
That's for sure. This is the main indicator of a real aggressor. An aggressor will abuse someone who loves him with even greater pleasure, it is even more "tasty" emotions for a sadist. Not necessarily direct physical violence, but the aggressor will necessarily belittle the victim's self-esteem, not to "treasure" them, but on the contrary - criticism of intelligence, appearance, any, even the most innocent actions. Astarion never does this, all his sharp jokes and irony are reserved exclusively for other companions, when did he mock or ridicule Tav? Not until after patch 6, when they decided to FORCE us to consider him the aggressor.
He is very sincere at the party in the epilogue. Look closely at his facial expression and the way he looks at you, he really doesn't want to let Tav go even for a little while. He is sad when Tav goes off to socialize with others. If we could still show our love for him properly, even if only by hugging or kissing him, I think his love would show even more vividly.
I almost wonder if the discrepancy can be explained by the writers focusing not on making Astarion outright abusive (patch 6 kisses aside), but on the desire to truly let the player roleplay the relationship the way they want, not just in their dialog options, but in Astarion's personality. If they want to roleplay as a regretful Tav who no longer trusts the man they fell in love with, Astarion will become an evil, possessive Dracula type. If they want to roleplay that they think his wickedness is great, actually, he basically becomes Lestat (from the second book onward) with more Machiavellian ambitions.
It's as if someone decided to "prove" - here, look your Astarion is an "abuser"! You didn't believe he was abusing you? Oh, he didn't insult you? Now he's going to insult you so much that you'll be insulted! You won't want to touch him again! For those who looked at this as a "cycle of abuse story" it lays into headcanons pretty well. For those who love Astarion, it's a real insult, a blow, and just illogical, delusional scenes. Even the Tav-victim facial expressions fit exclusively the version of that Tav who already thought Astarion was the aggressor, who hates and fears him, dreams of escaping but can't, and so on. If they wanted to show Astarion as a sadist, who hid it all the time, and "turned around" only when he got the power, then, firstly, if he treats the one he doesn't want to kill in such a way, he doesn't cause any real physical damage, only emotional damage (grabbing and pushing, in general, not painful), so he loves with such a specific sadistic love, it's a "treasure" after all, then what will he do with Tav, who didn't give him a chance to perform the ritual? The revenge will be sudden, very cruel and bloody. And naturally, such a sadist would do very bad things to other people who are not " favorite". Who will interfere with him, the Tav victim who fears him? Companions who depend on Tav the victim? He'd start deciding what to do himself, he'd start ruling right away, Tav wouldn't decide anything at all. Not to mention that the actual facial expressions of a person who gets their love killed and the closest person in the world steps a boot on their heart would be completely different than Tav's in those scenes. I think the "right" facial expressions for that situation would be too difficult to be realized.