I know John will start going out with other people. . . I'd rather see him going out with you."" So said Mrs. John Lennon (Yoko Ono) to 22-year-old May Pang in 1972--about two years after May, a N.Y. secretary at the Beatles-owned Apple Co., had begun working as the Lennons' much-put-upon personal assistant. May was shocked, she says, unwilling to sleep with her married boss to please the paranoid, manipulative Yoko. But then John convinced May that an affair with her was his idea--and ""the feeling of passion and desire that I felt for him overcame the guilt and awkwardness that I was also feeling."" Soon, in fact, ""as strange or incredible as it may sound,"" this Yoko-arranged liaison was a deep and happy one; Yoko felt obliged to leave, even if she insisted on keeping the real situation a secret and maintained quasi-control over John via a dozen daily phone-calls (heavy on lies and psycho-drama). But, though John showed some psychic improvement while in May's company (less drinking, more sociability), he remained ""complex and paranoid,"" alternately helpless and abusive, subject to violent fits when drunk, unpredictable when under Yoko's Machiavellian spell. And, after 18 months, Yoko announced ""I'm thinking of taking him back"" . . . and proceeded to do just that. Casting herself in the self-serving role of innocent-victim/Florence-Nightingale/starcrossed-lover (""Given the chance, I would do the whole thing over again""), Pang is not the most credible of eyewitnesses; while John and Yoko's craziness (extensively documented elsewhere) is sadly believable, Pang's own motivations--and her attempts at psychology--remain murky. Still, if the tortured love-affair itself often makes for tedious and uninvolving reading, Pang's descriptions of day-to-day life with the Lennons are sometimes grimly fascinating: Yoko's avant-garde filmmaking (cattily detailed); nightmare-like recording sessions with bizarre producer Phil Spector (one target of Lennon's noisy anti-Semitism); happier jam sessions with Elton John, Harry Nilsson, or--a rare moment--Paul McCartney. And, somewhat more slickly written than most such kiss-and-tellers, this uneven memoir will attract a certain portion of the Beatlemanic readership.