Not a Happy Day

I am so unhappy today. My 16 year old dog Noah is very ill and weak.
I hate the thought of losing him.
I raised him from a puppy.
I had seen an ad in the local paper for free puppies and went to see what they had. There were 6 puppies all running around in a fenced-in back yard. They were all playing and dashing about.
I thought, The first one that comes to me will be the one I take home. At that moment one of the pups ran straight to me and I picked him up.
So he chose me for a "mom" and I have never been sorry.
He has been a great dog. He is the gentlest dog I have ever seen in my life. There has never been any agressive behavior from Noah. He does not like to hear an angry voice and would quickly walk away from it.
Noah instantly loves everyone he meets and pushes his head under your hand so you will know he wants you to pet his head.
The only strange behavior he ever exhibited is paper-eating. That dog would pull kleenex out of a box, one at a time, until he had eaten as many as he wanted. I sometimes give him a few as a treat. My other dog just gives me an odd look when I offer him a tissue so he will know what Noah is getting.
He has always been the happiest of dogs, easy to please. A quick swim at a local pond or a simple stroll aound our yard always brightened his eyes.
Now he is just laying there on the floor, waking occasionally, lifting his head and looking around until he spots me. Then he puts his head back down. "I'm right here, puppy," I say to him.
My heart is breaking...