Endless Voyage — Marion Zimmer Bradley

Gildoran was an Explorer. Despite the number of planets found and tied into the Transmitter network that enabled everyone else to travel instantly from planet to planet, his home was his Ship, and the only people he could count on were her crew. For Explorers traveled through space to find new planets, and their years were decades or centuries to anyone not on the Ship. As they found and struggled to survive on unknown worlds, the rest of the Galaxy moved on, so when they returned to "civilization" anything could have happened, and the world they left was not the one to which they returned--even if it was on the same planet.