it keeps coming back beacuse it knows u have food. if u want to keep it around, just set out a bowl of dry food on your doorstep away from the other cats. the cat is feral, which means its a scavenger. it will do anythign for food. its learned that your place has food and it will do anything to get it, even if it means fending off other cats by beating them up. either leave some food out just for it or keeping it away by taking the food away