The spot where I put the band-aid in the picture keeps leaking milky white fluid, like breast milk, and it won’t stop.

The constant discharge of pus-like fluid from your cat’s belly likely indicates a deep wound infection, but because you’ve covered it with a band-aid, we can’t clearly assess the situation. I’d suggest first fitting your cat with an Elizabethan collar to prevent it from licking the wound.

Then take the cat to a veterinary hospital promptly for an examination. The vet may need to open up and clean the wound, then inject anti-inflammatory medication into it or use antibiotics systemically. A band-aid is useless for this kind of infection and will only trap heat and moisture, making it worse.