The poem makes a blunt claim: there is no bigger fraud than a promise not kept. It sounds like a firm moral rule, the kind of thing someone says when they have been let down. But the last line, "So am I a fraud?", turns the statement back on the speaker, and the whole tone shifts from judgment to doubt.
The speaker seems to feel guilty, or at least uneasy. Having set such a harsh standard, they now have to hold themselves to it. The question mark suggests they may have broken a promise of their own, though the poem never says what it was, so we can only guess.
The scattered layout does a lot of work. Words drift across the page with large gaps between them, so the sentence comes out slowly, almost reluctantly. The trailing dots after "Kept" add to this, like a pause before an uncomfortable admission. The mood is quiet, hesitant and self-questioning, as though the speaker is not sure they like the answer.