Sorry, that angel is seriously ill. Its eyes are cloudy and it is breathing really fast, and cannot get up off the bottom very well. The core issue could be a disease known as velvet, or it could be gill flukes. Given that you've had the fish for some time, I would say it is more likely to be flukes. It is VERY difficult to treat fish with severe fluke infections like this... you can give the fish a 5 minute freshwater dip and the flukes will all fall off, but then, there will be a hole in the fish's skin wherever there was a fluke, and if there are a lot of flukes, the fish will literally bleed out. Still, if you don't do anything, the fish is going to die pretty quickly.
Jay