I understand Tav may become a full-fledged vampire in the future, coincidentally.
I don't think Astarion will ever let them become one ('Trust me, it doesn't happen' line comes to mind). Even if Tav drinks his blood ingame, it doesn't change anything. It seems like he also has to willingly let them go while being drained for it to work. In the epilogue you can have a discussion with him about freedom and he gets annoyed about it. He fully intends to keep Tav by his side forever.
Originally Posted by Marielle
He truly loves Tav and wants her to always be there for him. And "giving into his power" is the only way she can prove her love. He gives a very serious and heartfelt thank you for that: "You gave me everything. Thank you" in such a tone that you can immediately sense how important and meaningful it is to him.
I adore that line and the way he says it. The whole time he's trying to persuade Tav to join him, he's clearly manipulating them. That's why his "I love you" doesn't sound very sincere because he is not expressing his affection but is forcing himself to say it to convince Tav. It seems like he feels awkward articulating real feelings and especially doing it right after ascending (when he feels almighty) puts him in a vulnerable position. The simple "thank you" to me is the real love confession. That's the moment where he feels 100% secure and calm and the scene is very intimate. There is no more need to put on a show and use fancy words. His feelings are actually very intense, just look at the way he watches Tav while drinking their blood just before thanking them!
