The Man in the Maze by Robert Silverberg 1977
This is the story of an honorable diplomat who bravely made contact with intelligent aliens only to be exiled to a remote planet, where he may be the only one who can save humankind.
Once a hero, now a pariah, Richard Muller is humanity's last hope.
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 that 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?