I'm so sorry. I am sure we all know the hurt.
Look up a poem called the rainbow bridge. It helped me several times now.
I'm not looking forward to losing the old guy I have laying in my lap right now. He's a 14 y/o mini poodle. He got bit when he was 4 months old, and got a spinal injury, that about crippled him completely. Front leg has been drawn up in a hook, and a high stepping rear leg. The hip is about gone, and now he drags himself. He's so full of love, and has been my lil buddy. Goes float tubing, on the boat, camping, and sleeps in my ARM pit.
It'll be a terrible day when he goes.