If I understand your question, it refers to the end of the story. Mr. Waythorn has gradually become aware through his encounters with the two ex-husbands of his wife Alice that she is not entirely the idealized angel of the home he has imagined her. He realizes that she has told him self-serving stories about her ex-husbands. For example, he sees that her first husband is a gentle, timid man, not the brutal man Alice had described.
At the end of the story, Mr. Waythorn has little reason to overcome his misgivings about Alice. However, it seems entirely in character for this man, so wedded to his comforts, to decide that his situation is not so bad after all. As he thinks:
If he paid for each day's comfort with the small change of his illusions, he grew daily to value the comfort more and set less store upon the coin. ... He even began to reckon up the advantages which accrued from it, to ask himself if it were not better to own a third of a wife who knew how to make a man happy than a whole one who had lacked opportunity to acquire the art.
The very last line appears to reaffirm his resignation to a tarnished ideal, as, meeting with the two ex-husbands in his home, he accepts his third place status:
She [Alice] glanced about for Waythorn, and he took the third cup [of tea] with a laugh.