Return of the Titans by Milford Slabaugh
Gay erotic novel, with frequent and explicit sex. A huge starship is heading for Earth, but this is no alien vessel; for these are Earth's ancestors, returning after many thousands of years of separation. Mankind of Earth has a lot to learn about its own lost history...and first is that the Star men are double the size of Earthmen! Our hero is an investigative reporter trying to learn all he can about the cousins of Mankind, and the secret he learns will change the Earth forever!