How long has this tank been set up? What other fish are in it and how many of each? How large is the tank and how big is the kissing gourami?
Also, do you know deffinately that it's a male? These fish cannot be sexed visualy unless they spawn - has it spawned in your tank? If so, what happened to its mate?
It worries me that you 'had the water tested'. You need to have your own test kit. if you don't, go get one immediately. Regardless, what were the parameters? I'm asking for actual values here - not just the 'everythin'g ok' that all LFSs will give you when they test your water and ammonia is at 5ppm!
What is the temperature int he tank also? And is your current strong? How's your pH? Have you added any wood to the tank altely - or maybe some plants?
For the time being, try feeding your fish some blanched greens such as zuchini and also get some frozen green peas - de-shell them and crush them before feeding. These green foods are essential components for kissing gourami diets (they are largely herbivorous) and will also prevent constipation.
Don't feed it anything for a day after that and then give it some live or frozen foods - eg bloodworm, brine shrimp or, better yet, some daphnia.
I assume the fish doesn't appear bloated, is not producing white/stringy poo and is acting perfectly normal besides the lack of appetite.