Apologies for horny. This pretty edgy topic, please, neat.
Astarion has a romantic side that is revealed in the game, in Act 2, his emotions and feelings. Yet Astarion has a freaky-decadence side to his personalities and sexuality. I will write what are the prerequisites for this in the game. Here is not a discussion, but my plan is to justify my suggestion.
My suggestion: Uncover the decadence, hedonism and power-control-play in Astarion's sexuality before and after the ritual. Astarion is a vampire, he enjoys blood. That's a lot of ways for an "Evil" romance too.
EA's artbook has it that Astarion is inspired by "18th century libertines", a prominent representative being Marquis de Sade. I don't think the original inspiration is rewritten.
One thought I had was that Astarion's sexuality is very much tied to control and power plays. He has... Moments of it. Like in everything, general.
The Marquis de Sade was confronted with the institutions of power throughout his life. He was the one who was judged, the one who saw the judgment and the one who ruled it. I won't reason on how right and healthy he was. He had a certain picture of the world. Morality, religion and law are all nonsense, there are clear roles in the world - the weak and the mighty. Everything is based on the power of the strong over the weak, but the roles are constantly changing - yesterday you are a powerful monarch, and tomorrow your head is already on the scaffold. Very much like the picture of Astarion's world: you either eat or you are eaten. Power is a tool to do whatever you want. The Marquis de Sade transferred those brutal realities, revolutions, executions and corruption to people's sexuality.
In game we have Astarion's approvals and reactions, and Dark Urge-thing, it's definitely interesting to reason about that. I think that's partly why we have the kneeling scene for Lord. He's gained Master status, now there's nothing stopping him from revealing his sexuality as a Master. This part of Astarion's sexuality could have been revealed in another scene with this kind of power play in more detail, before the ritual and maybe after for both ways.
Astarion is attracted to Tav outwardly, something he says himself. I would also like to explore the theme of his hedonism, which Astarion mentions a couple times. But Astarion begins to feel deep emotions because of Tav's care. These emotions, feelings cause dissonance with lustfull sex (which I think Astarion is experiencing), but deep emotions in this is ruined for Astarion because everyone who was interested in intimacy with him died like cattle. Control and power - I think that's part why he liked Sebastian, besides the fact that he was apparently nice, sweet. Astarion understood and controlled everything very well with him, because of his inexperience - Astarion decided how to kiss when, how much. There's a scene in the brothel where he refuses, or after the ritual in all cases still can't relax. Realistic, I'd just like to know the lines along which Astarion actually enjoys so I know what direction to go in next.
In both endings it's clear that there are two romance lines - Romantic and Decadence. Perhaps they blend together with each other in different parts. I'd like to explore Decadence one more.
I have a feeling the same problem is at play here as with the whole path of evil. It gives too little, yet it should essentially be another path to explore. In general, Astarion really dislikes being ruled, even when it's well-intentioned - and he likes to be the one who rules. To rule, to control, is also to protect, to be safe, but it's fun too.
Maybe Astarion can take great pleasure when he gets his hands on all the control over everything, with strict rules dictated by him and quite a bit of brutality. Maybe Lovitar's friend can help us. Such will be the romance for the Path of Evil.
There are some examples at the end.
Lovitar is the clearest example, Astarion is in thrill to the show of power. Of course, there's also blood, but he's interested in the show itself.
Approval for torture-things, it's a show of power strong-weak, predator-prey.
The whole conversation is about how to kill Tav if they start turning into MF. Astarion is engrossed in this conversation.
To Dark Urge. Astarion: Ssh, or I'll rush off and tell your Father you've been fibbing. Did he spank you growing up, or go straight for the cat-o'-nine? (maybe this was added for luluz's sake and Astarion is joking, but after some of his approval and dialog, it's not just luluz, I don’t think so)
The brothel has a line of Astarion's original. Player: Just don't tell me what to do... It brings back bad memories. (he puts limits right away, which is a bit of a hint + considering other examples)
Goblin Crusher-moment Astarion approves if the player submits for 5 points. 1 point if the player subdues a goblin. 1 Point if a player steals a ring and inspiration 1 Point if a player kills him. I wondered. Astarion 1 - Looks at how easy the player is to control, and he likes that, profit. 2 - in all cases: Fun, as he says.
Voice barks for Astarion Astarion: Maybe they like being restrained? Astarion: You look good helpless. Astarion: Oh I shouldn't laugh. - The character is in a Romantic Relationship with him, unconscious or immobilized.
