Just checked him out this morning and he's died ;_; iv'e done a 30% water change and added Melafix medicine (curing ulcers on a zeebra leopard) poor thing.
If heard of sunken eyes in relation to TB and other bacterial illnesses (in which case keep a close eye on your fish) and malnutrition in particular....
Did the Gourami take his food readily?
What did you feed him and how often?
Sorry for your loss