Narcissa black married down,any marriage for her as a black would be marrying down. But nonetheless she married down and when ever Lucius is a dick he will always be remind of that fact, if that is by the other children of the black, or the rosier cousin, or on the the rare occasion narcissa herself. He will never have full control over the marriage as he wants because narcissa could divorce him and have very little backlash as she is a black. And no one ever would dare to deal with the blacks, they’re crazy.