Okay hear me out... vampire bride Halsin.
Halsin is wrecked when the party comes back from facing Cazador and he learns his new love sacrificed thousands to an archdevil in exchange for unknown power. He lost the Astarion he loved, but it’s Halsin, so he doesn’t break things off. He just leaves it be and does what he can to cling to what's left of the old Astarion when they are together, spending even more time with the refugees and running off to Reithwin once the Absolute is dealt with. He's needed, it makes him happy, Astarion has all the time in the world to wait for him to come crawling back after his fun. But he doesn’t. A century passes and Reithwin is on the map again, no longer a black smudge of curse, and thriving. But Astarion’s survived the attempts on his life, and all this power of an ascendant trickling in gave him the knowledge of brides centuries early. A Dark Kiss, how romantic. He knows what he must do the moment the ritual comes to him.
Halsin is not a hard man to find, even without money and power. But a little coin and strings pulled left the druid once more kidnapped, though this time without harm. Astarion takes his time as his love is still unconscious from the kidnappers' drugs. One bite. Two. Three...
Astarion half forgets himself as Halsin wakes, mindless and feeding during the ritual. He’s an animal, a beast, and now a creature of the night, and it fits his love so well to be so feral. Wanting, no, needing him so desperately. But the ascendant pulls himself back into the moment soon enough to break free and keep from being drained in the ritual. Halsin sleeps as he turns pale. Astarion finds such rest so beautiful a look on him...
When Halsin wakes up, he is confused at his surrounds, but Astarion is there. He just missed his consort, that’s all. It's a forced vacation for a man who never rests. Relax, darling.
Halsin wonders why he craves raw meat so much… But yes, he can try to enjoy a break to please Astarion. To once again try to find the man he fell in love with, or at least taste the pieces of. Then he can return home.
Astarion keeps him inside for a long while. He's glad Halsin isn't a man of vanity as he had the mirrors put away. Every time Halsin wishes to go outside while the sun is up, Astarion pulls him away for sex. He keeps Halsin fed despite the food not being what he really needs, suggesting raw meats as much as possible and having blood dripped into whatever the servants can hide it in. In time he will learn, but not yet.
Halsin dealing with constantly being hungry but food doesn’t taste right anymore. Doesn’t satisfy, not even honey. Must be his nerves of being suddenly taken, suddenly back in the city he nearly died in years ago, with what remains of his partner -- if he can even call him that anymore. Or perhaps the drugs used to get him here messed with him more than intended. He isn't quite sure...
Astarion finally goes for a walk with him to the park at night “when there are less people about so you can enjoy a bit of peace in your beloved nature.” Halsin can’t get the hunger to leave his mind. He loses himself when a rabbit darts by, near-blacking out as he snatches it in but a moment and bites down. Somehow this raw meat has flavor finally. He’s still hungry. Astarion teases that the bear truly is a beast. Halsin apologizes for the display, he hasn’t felt himself since waking in the city. Astarion says he has nothing to feel sorry for, he quite likes the view. Halsin could stand to lose himself to the “beast” more often. Relax, darling.
Astarion carefully feeds into Halsin's primal side. The bear, the beast, the more natural and feral part of Halsin that Astarion insists is better. But he also carefully isolates him. He doesn't want to be out in the day when all the horrid people are out: Baldur's Gate isn't so different from last time he was here. And Astarion doesn't want Halsin to be sad about the state of the city, not at all. Stay in the palace with your love and have a nice time. It's a vacation, remember? Relax, darling.
He slowly pulls Halsin back down into a cultivated depression. Nature is out of reach but for his own feral instinct and the occasional night walks. Silvanus and Thaniel grew quiet a long time ago. The rats under the palace that Astarion calls pests are attempted friends of Halsin, but he keeps losing himself in fits of hunger. They are not safe around him, so he doesn't even try anymore.
Once Astarion feels his bride is sufficiently calmed, only then will he begin to explain to Halsin his new undead nature. Once Halsin doesn't have it in himself to care. When Halsin's sanity won't break at such a revelation. Then Astarion can build Halsin back up. He can make sure he has the happiest bride in the world.