I've only seen the Kubrick adaptation but it was very heavily implied that the narrator is impotent. He's shown to be a character to be laughed at, nervous in his behavior, and quite hapless in romantic overtures.
Contrast that with the movie Pretty Baby where the main character becomes obsessed with a 12 year old prostitute and then sleeps with her. I find that movie to be more bordering on the obscene than Lolita.