With the exception of John Ray, Jr.'s academic and self-important prologue to the memoir, the novel offers one point of view, one voice, and one side of the story: that of Humbert the victimizer, whose skill with language surpasses just about any reader who comes across the novel. Humbert's superiority (to Lolita, to everyone, to the "jury" he dramatically addresses from time to time, and to us) is something that Humbert banks on.
Humbert is about as far from a reliable narrator as can be. He has had numerous stints in psychiatric clinics. One example: "A dreadful breakdown sent me to a sanitarium for more than a year; I went back to my work—only to be hospitalized again" (1.9.1). The reasons he gives for his four recorded "bouts of insanity" are "melancholia and a sense of insufferable oppression" (1.9.5), a "sexual predicament" (1.9.5), and "losing contact with reality" (2.25.5). These are what we call narrative red flags: the guy is nuts.
Still, Humbert the narrator is the ultimate manipulator and seducer, extending his skills to his storytelling techniques. He teases the reader with hints – "a bad accident is to happen quite soon" (1.19.1) – and makes constant direct addresses to the reader, saying such things as, "Ladies and gentlemen of the jury, exhibit number one" (1.1.4) and "I want my learned readers to participate in the scene I am about to replay" (1.13.5). He also provokes the readers: "Let readers imagine" (1.15.3), wanting them to enter his mind, which itself does a lot of imagining. "Imagine me," he says, "I shall not exist if you do not imagine me" (1.29.5). He wants the reader to envision, invent, participate, approve, and speculate. Keep in mind that his lawyer has prompted him to write this account, which unfolds as a strange combination of self-incrimination and self-defense.
Bottom line: we cannot trust a word he says.