By JOCELYN NOVECK and ANDREW DALTON LOS ANGELES — After a relationship that spanned two decades, two engagements, two weddings and headlines too numerous to count, Jennifer Lopez has filed for divorce from Ben Affleck. The filing Tuesday in Los Angeles brought to an apparent end a celebrity coupling — or at least the second installment of it — that dazzled from the very heights of the pop culture firmament and emblazoned countless tabloid covers.