Who is May Bartram from Tales of Henry James: The Texts of the Stories, the Author on His Craft, Background and Criticism and what is their importance?

May is the faithful friend of John Marcher, the only person that he has ever told about his obsessive belief in his destiny. She loves him, and lives simply in a small house in London on a meager inheritance. It is May who first realizes that the great event in John Marcher's life is that nothing noteworthy happens to him.