It had not occurred to Marian that when the success for which he struggled began to come generously, Eileen would begin to covet the man she had previously disdained.

She had always striven to find friends among people of wealth and distinction.

How was Marian to know that when John began to achieve wealth and distinction, Eileen would covet him also?
Marian could not know that Eileen had studied her harder than she ever studied any book, that she had deliberately set herself to make the most of every defect or idiosyncrasy in Marian, at the same time offering herself as a charming substitute.

Marian was prepared to be the mental, the spiritual, and the physical mate of a man.
Eileen was not prepared to be in truth and honor any of these.

She was prepared to make any emergency of life subservient to her own selfish desires.