You are sucking a bunch of air from somewhere.
My guess is the carbon seal is toast, but a full inspection of the pump will need to be done.
If it was me... since the cavataion is so bad... I would order a new carbon seal, boot, and ring. (and the o-rings) Also, I would get a new pump neoprene gasket, and wear ring. Take the pump off, and replace those parts, and it should take care of your issues.
Even if the impeller is beat up... you should be OK as long as it isn't destroyed.