Outcasts: Beginnings - Outcasts, #1

Rem is happy with his life as a whore. He gets to travel the universe, meet all sorts of new people, and make more money than he knows what to do with. When his boss offers him a ridiculous sum for a unique job, he jumps at the chance. The job entails pleasing four aliens during a month-long excursion to the edge of the known universe. As the only human aboard, Rem has a lot to show his clients-- and a lot to learn.
But life is never boring amongst the hardened Nihir, the delicate Tu'Van, playful Ellam, and the ever-watchful Creaik. But the more time passes, the more immersed Rem gets, and the more he wishes he could stay...