What the. As if it's not his victory too. I think someone on the writing team might be a bit too much into angst.
He does say later, he came to the conclusion, it was their victory.
Still, for me that line seems to put the blame (for hiding alone in the shadows) on Astarion. As if he had deliberately chosen it instead of the player being held hostage by the writing.
All I want for the dock scene is the companions to either say something helpful or say nothing at all and the option to follow him.