Cazador would have had to agree to let Astarion drink his blood for Astarion to become a true vampire. Or so Astarion believes. It's entirely possible this is something that is tied to the vampire's control over their spawn (they can't bite their master without permission), and Astarion could've forced it by just draining Cazador, but he doesn't think it would work, and the game doesn't work that way (if you ascend Astarion, let him turn you and then bite him, you won't become a true vampire for example).
It's possible that Astarion doesn't give the player all the information about the change into a true vampire either, only the short, simplified version. Currently, it looks like a plothole and I wish it was addressed and clarified how it works exactly. Since we can only make assumptions, I believe that he does not only need to drink the blood, but also be given permission to actually drink it with the purpose of becoming free and the vampire lord consensually relinquishing control of the spawn in the process of being drained. This would explain why Tav can bite Astarion for sustenance or intimacy but won't stop being a spawn.
I also don't believe he really doesn't remember anything from his life as a mortal - Cazador being there at the moment of his demise is very convenient and although the artbook might be outdated, I still think he was involved in some shady stuff that involved vampires, and just doesn't want Tav to know about it, so they're more willing to help him out and be sympathetic to his cause. But that's a whole different topic altogether.
Originally Posted by Nyloth
I would like if romance with Ascended Astarion to be like this...
They're both happy. I don't know why writers decided to use some kind of image "abusive asshole" and "his victim" While these are card from MTG and it clearly show that DnD vampires can be happy together. I don't understand why the "realism of toxic relationships" didn't work with Minthara, whose relationship is also unhealthy, but it worked with Astarion. It's terribly disappointing.
MTG has some really amazing artwork when it comes to vampires, and it's how I imagine this couple to be like. I don't care that the writers hate AA, I will still roleplay the relationship as happy and harmonic, as much as the game allows me to. My Tav went into it knowing exactly what she was agreeing to, down to sensing his bs about willing to turn her into a true vampire later ('trust me, it doesn't happen' line is quite memorable after all). She gave Astarion everything and he gave her everything she wanted in turn. At least I can call him 'my love' as his spawn now.
