BUT that brings it back to the relevant topic of the thread. I agree with @celesti. I'm actually surprised how...non-possessive he can be as a Lord. I wouldn't mind him being a tad more vampiric and obsessive in the face of poly scenes and dialogue. I'm surprised AA is so permissive and "do what you wish" with Tav. Compared to normal vampire lore, he is pretty soft with the PC. Not necessarily a bad thing. But couldve been fun to lean into the obsessive nature a bit more.
I agree it would have been fun imo and they wouldn't have needed to go overboard with it, either.^^
That made me think of this line that he says the morning after the turning night:
"
Just... don't stray TOO far – but you would never dream of doing that, would you?"
When he says the first part, he sounds kind of worried and uncertain, and I feel like that's because he knows Tav *could* stray from him if they wanted to, and he really doesn't want that to happen. In the second part of that dialogue (where he makes a slight pause and then says "but you would never
dream of doing that-") it seems like he catches himself and then puts on the self-confident air again, as if he's very sure that Tav's not going anywhere.
But to me, this was one example of the writing showing that he has possessive tendencies and doesn't want you to leave his side, at least not too far or for too long. The 'sequestering you' dialogue also comes to mind.
According to the vampire brides lore, the brides are actually convinced they can be controlled when in fact they aren't, so... The fact that Astarion can't bring back Tav, who broke up with him or left to hang around the Astral Plane, speaks volumes.

I personally lean more towards the vampire bride theory and I think there are enough clues there to make it ambiguous (if you'd like to think Tav is a regular spawn or if AA actually performed the vampire bride ritual on them, that is up to the player to decide in the end).