It is an interior monologue. It tells of Prufrock's feeling towards woman and society. The imagery is of Prufrock reciting the poem to an audience. It explains it in the epigraph, which is taken from Dante's Inferno.
Yes: the 1917 Prufrock and Other Observations (includes "The Love Song of J. Alfred Prufrock"), the 1920 Poems (includes "Gerontion"), and the 1922 The Waste Land are in the public domain. Later works are still protected.