Leave him alone, keep the water up and good luck.
I hope he pulls thru.
I had one that I took back to the lfs because it was on a hunger strike.
I did not want it wasting away in my tank.
If you have that option, it might be the best thing you can do for yourself.
Sry, that looks like there's definitely something else going on with your naso. Probably could use some sort of antibiotics but this would be the point where I'd be posting for opinions too so I'm out on specific suggestions.