Hellflower

Once He had Been a Star Master—Now He Dealt in Soul-Shattering Ruin... Farradyne had committed the one unpardonable error a Space Master could make. He didn''t die along with the other 32 passengers when his ship smashed into the Bog on Venus. They broke him—exiled him to the rotting fungus fields of Venus. Now his only desire in existence was to return to the cool, gleaming sea of deep space. And there was a way—only one. But he would have to become the vilest parasite in the universe—peddler of a poison that stripped the spirit, before it consumed the body...." (Goodreads)