I am so sick of the whole 'Lucius married Narcissa for convenience' thing. I want to see a new angle for once. We have canon proof at the end of the last book that Lucius was very protective of Narcissa and Draco, so that he genuinely loves his wife should not be a stretch. I do believe, however, that Lucius does have extra-martial affairs, but that he's very discreet. I'm sure Narcissa doesn't wholly approve, but I've had discussions at length with people about British aristocracy and this seems to be the norm.