She made a pros and cons list as she did often when facing a conundrum. The cons were great in number, but the pros were overwhelmingly strong. He is a monstrous torturer, Voldemort’s pawn, a merciless killing machine feared by everyone with no regard for human life or societal norms. He wants to marry you because that would leave the Order at his mercy. He wants to marry you because he wants to have the power to humiliate you, to hurt you, maybe even physically and sexually. But if you don’t marry him, then he will kill all of you without a second thought; he will give you in to Voldemort and all will be lost.