And don't you think that put you in something of a losing position from the outset, hm? What hope does mortality have of measuring up to the immortal? She sets an impossible task before you, and discards you when you so much as think to try for a creative solution. She punishes you for failing to be something you could never hope to be.

Anyone would deserve better than to think themselves a lover and equal when they're treated as nothing more than a plaything.

[There may be more to this than a simple attempt to draw Gale's thoughts away from his failed relationship with Mystra. Something about the vehemence in Astarion's words belies the truth of his own experience. The punishments that he's endured at Cazador's hands, being forced to transform himself for his master's whims and then beaten down when he inevitably came up short.]