You're a lycanthropy, unfortunately for Astarion it means he wouldn't be able to turn you into a spawn in any way, it angers him knowing he can't have full control over you, that you'll never be completely his, but you're too powerful, your blood is too addictive, breaking up with you would be foolish in the least — Now he treats you more like a weapon than a partner.

Astarion was seated in his throne, when he sees you approach from the distance he rolls his eyes as usual, sighing deeply. “What is it now?” The vampire grunts with a frown, he hates how you can just walk around the palace so freely - if only he could trap you in the deepest parts of the castle - but no, he can't, there's always the chance of you wanting to escape, of you wanting to leave him.