The worst thing with Astarion (wether Spawn or Ascended) that he hasn't fully realized the horrors of what happened to him. Right now he is happy and hopeful... but the weight of 200 years of abuse and misery is only yet to fall on him. Once he sees the world outside the walls of Baldur’s Gate he will realize how terrible it was for him.
And it will be yet another round of hell for him. Maybe even worse because now he is free and he has nothing to complain about. I am sure he will trey to make Tav make decisions for him because he lacks the ability to do so and his past will torture him forr decades and decades.
Astarion thinks the worst has already happened.
But he will have to go through a psychological purge soon