As it stands, the last line of the narrator's claim hardly seems believable in light of his admissions about the other woman.
In the story, the narrator finds himself infatuated with a woman who is not his fiance. In all other respects, the narrator's life is going very well: he has just been given a highly coveted government position, and his achievements as a poet have been greatly lauded. Furthermore, he is about to be married to a wonderful woman he greatly admires. Yet, he finds himself drawn to a seemingly ordinary woman who is already married, a woman supposedly beneath his notice .
We get a glimpse of the narrator's often tempestuous thoughts about his affair through the stream-of-consciousness style of his narrative. His thoughts jump from one sensory description to another. Although he tries to put the other woman out of his mind, he can't help but connect her with any 'noble thoughts' he tries to have. Indeed, his confusing narrative style seems to mirror his sexual frustration. When he imagines the other woman in bed with her husband, he becomes incensed. He tries to sleep but the sexual tension drives him mad:
I tried to think of the woman I loved, but her figure had also become something far away, something with which I for the moment seemed to have nothing to do. I rolled and tumbled about in the bed. It was a miserable experience.'
The rolling and tumbling suggests the sexual passion the narrator would like to engage in with the other woman. It is evident that his thoughts equate sexual satisfaction with a woman who is not his intended fiance.
Furthermore, his fiance's statement in a letter is telling:
For a long time, after we are married, we will forget we are a man and a woman. We will be human beings... I will love you tenderly and passionately. The possibility of that is in me, or I would not marry at all.
Here, the narrator's fiance equates marriage to an egalitarian partnership. That much is clear; however, one can also infer that her statement betrays her possible fears about her own sexual responses to her husband. Later, when the narrator speaks of his fiance (and then, his wife) he uses the word 'awakening,' which gives the impression that his wife is not yet awakened to the potentialities of her own sexuality, but is open to the possibility of it happening, as can be inferred from her own veiled statements in her letter to the narrator. This, in part, explains (though does not excuse) the narrator's obsession with the other woman. It is the sexual availability of the other woman which has entranced the narrator.
The narrator also lets on at the end of the story that his wife does not share his bed, but sleeps in the room next to his. Even while he purportedly thinks of his wife in bed, he confesses that the other woman still claims a portion of his thoughts. He describes their sexual escapades as being the 'most notable experience' of his life and that, when he was with her, he felt closer to her than to anyone else in his life. It is obvious then, that the narrator's statement about the other woman being gone from his thoughts when he awakes does not seem at all believable.