There are a couple of issues at play here, as noted by other members. The internal health issue is one, I leave those issues to members more knowledgeable in disease/health issues, so follow Colin's advice. But the stress issue is certainly another problem.
The background was mentioned and this is very important; the presence of a dark (non-glossy black is ideal, like construction paper taped on the outside) background is much more important than many realize.
The other issue is the surface...gourami must have floating plants, it is an expectation because that is the habitat they live in and providing similar will always make them feel more at ease. Substantial floating plants, like Water Sprite, Water Lettuce or Frogbit are ideal here and will make a huge difference to the gourami.
Third issue has also been mentioned, the normal hierarchy of a group of a gourami species. All males are territorial, the degree to which they enforce their territory depends upon the species, individual fish, and the environment (aquascape). This could be a factor, if for example the quiet fish is a male and another male is making it clear that he owns the space. Sit quietly without moving in front of the tank of a period of time, sometimes half an hour, and see if there is any interaction between the gourami. Males also can get "pushy" with uncooperative females, another aspect of interaction, as well as male-male dominance.
