There is a thread in Gen Freshwater about another sick gourami....the consensus, I believe, is that Gouramis, especially Dwarf Gouramis, have been "messed with" so much by selective breeding, adding stuff to their water and bodies to make them flashier looking, that its seriously weakend the species. Or at least, the ones regularly available. They are now very prone to all sorts of parasites and diseases. Its so sad, this happens every time a breed or any species becomes popular. Backyard breeders abound, trying to make a few dollars, and the animals are the ones who suffer. I have been wanting to add a D. Gourami to my larger tank for ahwile ,but now Im not so sure. They sure are beautiful fish though!
I dont have much advice for you though, sorry. Just keep his water nice and clean by doing water changes every day or other day. Have you medicated him with anything?