Who knew the SEC had such humorists on its staff? South End author Scott Pomfret, who hunts security defrauders for his day job, refuses to abandon the Catholic church any more than he wishes to become straight and therein lies the dilemma at the root of the book he will read from at the South End Library tomorrow night. It is sprinkled generously with shaded sidebars demystifying practical matters about gay Catholicism to the uninitiated ("Where the Hell Am I: A Guide to Church Geography," "How to Come Out to Hard Core, Bead-Counting Catholics," "Excommunication FAQ," and "The South End Catechism") with a sighed acknowledgment that for many Catholics it is a "religion of screwy, random rules with fantastically grave consequences." Pomfret takes on Archbishop Sean O'Malley during the gay-marriage debate in Massachusetts with passionate and articulate letters he hopes will convince the Church of the error of its ways. We know the outcome but Pomfret keeps hope alive. At the South End Library.