Um, FE...one is incest, the other basic cheating that happens all the time. Not comparable. Even if Maddie was just another woman who was not related to Jean or Nate, it would make Nate's situation seem much more disgusting for sleeping with a woman who looks like his mother.

Scott's situation is only deviant because he used Maddie as some morbid living memory of Jean. Without that, it would be like dating her twin, which is very common.