When does Astarion say this? I've heard of it but I didn't have it in the game, can you tell me in which dialog this line is in? I remember Ulma's lines - it's when talking to her in the gur camp.
I think it's unrelated to Ulma- he says it when you ask about his story. Here's the dialogue branch:
Astarion: I suppose you want to hear about Cazador.
(...)
Player: Not a good master, I take it?
Astarion: He had me go out into Baldur's Gate to fetch him the most beautiful souls I could find.
Astarion: It was a fun little ritual of his - I'd bring them back and he'd ask if I wanted to dine with him. And if I said yes, he'd serve me a dead, putrid rat.
Astarion: Of course if I said no, he'd have me flayed. Hard to say which was worse.
IIRC, this iteration is kind of specific, I've definitely had it in EA a few times, but I can't nail down what kind of situation triggers it right now. I think it's if you haven't discussed Cazador at all, and then you discover about him. When you talk to him, he directly brings up the topic.
