animal laws URGENT!!!

PLEASE there is this old cat it is a stray that decided to live around our house. we gave it a shelter outside and food on a regular basis. the cat has recently become very ill and is craping all around the house out side and i am sick of cleaning it up. we have very little moeny and no resorce to get him put down. the cat is craping blood and i cant take it any more. i really need to know if it is legal for me to kill my cat a bury it on our property. please dont get me wrong i love animals but i have just finished cleaning crap stains off the pourch for 4 hours straight!!!! - Is this your question? Add additional information