Your gourami might be sick because of its water conditions. Gouramis are very sensitive to changes in water quality. If you haven't done a partial water change in a wile you might want to do that but by doing this your taking a chance that your gourami might get stressed out and die. The best solution is to separate your gourami from the other fish and keep the aquarium light off to reduce stress. I hope your gourami gets better.