PAPERBACK. EDITION--=MID SIZE SOFT COVER-WILL COMBINE BOOKS TO SAVE POSTAGEUpdike's eighth novel, subtitled "A Romance" because, he says, "People don't act like that any more," centers on the love affair of a married couple in the Connecticut of 1962. Unfortunately, this is a couple whose members are married to other people. Suburban infidelity is familiar territory by now, but nobody knows it as well as Updike, and the book is written with the author's characteristic poetic sensibility and sly wit.