I really have to put my cat down.
Why would you want to put your cat down?
He is sick and drying.
It is ok to not want a pet to suffer while they are dying. You should take them to a vet and see if they can be saved first.
They said that he is dying and there is nothing they can do.
I hope you can spend some time with your cat before he goes. Have you set up the appointment yet? The sooner you do it the less suffering they will go through.