Author's Notes: Written for dallirious for the rarepair_shorts Summer Wishlist Event, with the requested pairing Rodolphus/Narcissa and the prompt "couldn't, shouldn't, wouldn't".
When Rodolphus and Bellatrix had been married, he had thought it the best possible match – he had been enamoured of her and she was at least somewhat fond of him. The Dark Marks freshly emblazoned on their arms gave them one more thing in common – if nothing else, Rodolphus was her partner as a Death Eater, and she could appreciate him for that. It had been far from the perfect match, but then, a perfect match was all but unheard of in their families.
But Bellatrix began to spend more and more time in the company of the Dark Lord, instead of her husband. She rarely spoke except of matters concerning the Death Eaters. The happiness and promises of fidelity that had been repeated so often during the honeymoon were forgotten – or, at the very least, Rodolphus suspected that they were.
But perhaps it did not matter; perhaps it was all for the better. Perhaps, if Bellatrix had found someone that she preferred to Rodolphus, he too could find someone.
Someone like the little girl who had hovered about the balls and parties that he had attended with Bellatrix and sighed over how terribly romantic it all was. Someone like the little girl promised to Lucius Malfoy.
When Rodolphus was alone – his wife far away and perhaps with the Dark Lord; perhaps simply not with Rodolphus which was every bit as bad – it was the image of Narcissa Black that danced before his eyes, and it was when he saw her that his breath hitched and his heart sped the way it had with Bellatrix before they had been married.
And surely Narcissa could not be ignorant… she smiled so sweetly at Rodolphus, spoke to him in tones that could not be taken to be anything but flirtatious…
But he couldn't. He shouldn't.
He wouldn't, he told himself over and over, every time he saw Narcissa and felt desire for her (far too often for comfort). He would not have his wife's little sister, no matter how willing she was and how much he wanted her.
He insisted that to himself when she smiled at him, when they were the only two people in the house, when no one would ever know…
When morning came, Rodolphus so often found himself lying abed with Narcissa's head on his chest and a sickening feeling of guilt in his stomach.