Robert Silverberg 
Man in the Maze 

A diplomat who successfully negotiated with intelligent aliens finds his loyalty to the human race tested in this novel by a Nebula Awardwinning author. Richard Muller was an honorable diplomat who braved unimaginable dangers to make contact with the first-known race of intelligent aliens. But those aliens left a mark on him: a psychic wound that emanates a telepathic miasma his fellow humans can neither cure nor endure. Muller is exiled to the remote planet of Lemnos, where he is left, deeply embittered, at the heart of a deadly maze … until a new alien race appears, seemingly intent on exterminating humanity. Only Muller can communicate with them, due to the very condition that has made him an outcast. But will Muller stick his neck out for the people who so callously rejected him?