Originally Posted by EMC_V
To me, that is because lack of choices/options. Excluding drinking the drow blood, Tav/DU is not allowed to ask "What do you like? What do you want?". The scene in the graveyard works because he is the one saying he wants to bury his old self and a new life. And he is the one asking for sex. He wants that but respect of Tav says no. The problem is that at the end, he asks what Tav wants, but Tav can't ask him back so if feels more like a common decision. And he doesn't have more interactions or a closure quest like Shadowheart. He is not shown doing things on his own initiative.

Player dialogue lines for Astarion are little bit terrible in general. Next to Astarion's beautifully emotional lines the player's words often have a cool detachment to them even when dropping the L-word. It just creates an imbalance when he thanks you for all the things you have done for him, but your character cannot reply in kind - and I am sure you can come up with something for all the Origins including Durge. Allowing the PC to be vulnerable or appreciative of Astarion as a person (not of his moral decisions) would do wonders - in my opinion at least. ^^ But I am a broken record on that topic.