by ERICH SEGAL
46 pages. Harper & Row. $4.95.
Once upon a time, a writer who was not really a writer but a moonlighting professor of classics at Yale produced a phenomenal bestseller called Love Story. The book had the texture of moist Kleenex, but it was bittersweet and it brought the professor wealth and fame, which he professed to dislike. He gave an endless series of farewell interviews and accepted one absolutely final nonscholarly job after another, from doing TV sports commentary to acting in movies. Yet did all this help him...