I think for a lot of men in positions as powerful as Lucius, cheating is just part of the lifestyle. But he wouldn't have an special loyalty to those he cheated with, either. Image is everything to a guy like that, and that includes the trophy wife and the strong family front they put on for the world. I can see him letting go with Narcissa, definitely. That's what her purpose is in the marriage - to provide comfort to him.

Lucius' strongest loyalty is to himself, I think. And I do agree with everything you've said.

Nice work on the H/D story by the way.