The Reef by Edith Wharton

Anna, the next day, woke to a humiliated memory of the previous evening.

Darrow had been right in saying that their sacrifice would benefit no one; yet she seemed dimly to discern that there were obligations not to be tested by that standard. She owed it, at any rate, as much to his pride as to hers to abstain from the repetition of such scenes; and she had learned that it was beyond her power to do so while they were together. Yet when he had given her the chance to free herself, everything had vanished from her mind but the blind fear of losing him; and she saw that he and she were as profoundly and inextricably bound together as two trees with interwoven roots. For a long time she brooded on her plight, vaguely conscious that the only escape from it must come from some external chance. And slowly the occasion shaped itself in her mind. It was Sophy Viner only who could save her -- Sophy Viner only who could give her back her lost serenity.