If you have a more accurate info that says otherwise feel free to link me. I'm open to change my opinion. But right now i'm more inclined to believe it bc after getting the spawn ending the two routes do feel like it's written with two different premises. And I think people have the right to be upset after playing the game with certain assumptions. I can bet there would be an outrage as well if Larian changed spawnstarion to be monogamous.
Interview with Stephen Rooney. He mentions they always had a clear idea of where Astarion's story would go and they wrote a "good" and an "evil" ending for the character.