Love, Jack

Like termites, JFK's old friends and lovers are coming out of the woodwork to tell their own ''true'' story of what really went on in the President's mind. The latest is a Swede whose affair with Kennedy began with a chance meeting in 1953, was consummated during a weeklong idyll in Scandinavia, and ended many letters later with Jackie's first pregnancy. Gunilla von Post, whose self-serving account with Carl Johnes, Love, Jack, is written in romance-novel prose, claims to have realized she could write her memoir only after Jackie died and that even then she wondered, ''Would her children understand? Would mine? What would people think of me?'' I can't speak for the younger Kennedys or Von Posts, but this person, for one, doesn't think much. C