Am I too argumentative again? I am sorry, I can stop, if you prefer. I get the feeling that discussion these days often just means agreeing.
I think, "I love you" "I am in love with you" is a nice thing to say. It tells the other person that they hold a special place in your heart, but that's about it. It makes no statement about which gravity this feeling holds for you - some people use it lightly others don't, the Astarion romance even makes fun of it in the beginning. The "you are the one I love, the one I want" and Astarion's "I love you, I love this" are well suited for the graveyard scene as a sealing of the bond, as a confirmation that you are in a proper relationship now, but they don't have gravitas.
What I mean by that. As an example: I romanced Astarion with Gale. During his audience with Mystra, he has an option to tell her that his new love is the reason he defied her orders. How great would it be, if he could tell the same to Astarion? For me telling Astarion you defied your goddess for him, that the only reason you are alive is because he reached out and gave you something to live for, holds much more weight than another "I love you". And I am sure that for all the other Origins and Durge you could find similar points in their personal quests in which Astarion has been the character's saviour.
Even telling him how scared you were for him when Cazador zapped him away for the ritual would be nice. It's a shared memory that could be used to show that you can really overcome difficult situations together, without needing the power of some devilish ritual.
