Agree with G&S – it sounds to me as if your horse is in pain, and it is getting worse. One question – why do you feel you need to longe (it is a French word, “lunge” is incorrect) him at all? Is there some purpose? You might be better to work him in long lines (driving reins) instead, to improve his flexibility if that is your goal. Being on a longe line is boring, doesn’t really accomplish anything that cannot be done in some other way, and I see little point in it. However, I am really, really prejudiced because of my own horses and their attitudes. A chain over the nose is really, really drastic – might have been better to use side reins. It seems to be making the experience unpleasant as well as painful.
It is never the horse's fault