The writers aren't trying to impose a position on your character, they've constructed a narrative because it's a story. The choices you're given reflect the intended narrative themes. The crux of Astarion's story here is about whether he will break the cycle of abuse or continue it. The romance is only potentially a part of that and his story exists outside of it. It's an authentic portrayal of the varying ways abuse and trauma can affect people, and they never pull punches with how ugly and corrosive that can be at any point in Astarion's story. They're not going to do it at the conclusion which is meant to be a brutally honest portrayal of the cyclical nature of abuse. It's a very well written and poignant narrative conclusion to his story and a valid path to choose. That's not to say anyone is wrong for enjoying or being attracted to this version of the character. They're not. But what's being asked for here is a different version of the character and story they've written.
Finally a sane answer here.
10 logical counterarguments have already been given to this answer.
