The speaker describes their journal in a string of odd, compressed comparisons. It is a lone shoe, something incomplete, missing its pair and not much use on its own. It is also a "little wife," a companion that listens and puts up with complaints. Then it becomes "a better ever after," a place where life might turn out kinder than it does outside the page. The last line gives the poem its sting: this is the thing "to which I bitch." The speaker uses the journal mainly to complain.
The title, "Never say diary," suggests the speaker wants to keep some distance from the word, perhaps because it sounds too private or sentimental. The tone is wry and a little self-mocking. The speaker seems half affectionate and half embarrassed about leaning on a notebook this way. The mood is dry, funny, and slightly lonely, since the one who answers every grumble is a page that cannot talk back.