I've about decided Libby's "niceness" was an act. There may never have been a sailing husband named David. Instead she seemed to almost be a serendipitous encounter for Desmond who got his boat out of it. It may have all been planned to get Desmond to the island.

__________________
Things fall apart, the center cannot hold;
Mere anarchy is loosed upon the world,
The blood-dimmed tide is loosed, and everywhere
The ceremony of innocence is drowned;

--Lines 2-6, "The Second Coming" by Wm. Butler Yeats