Hi Brian,
So sorry to hear the sad news about your friend. The bond we share with a dog is very profound. The burden and pain that comes with the decision you have had to make is very likely one of the more difficult situations you will face in your life. It hurts because they mean so much to us. Unfortunately there comes that time when the best we can do for them is to let them go. It is the ultimate act of love and devotion we can show them. And as everyone has attested to, it just does not get any easier. Through your sadness you must remind yourself of the rewards of their companionship. And that lasts forever.
I have never been without at least one dog so I am no stranger to the intense loss you are feeling. Over the last 20 years I have rescued 5 dogs and feel I have gotten far more than I have given so there was nothing I would not do for them. Each of them have touched my life immeasurably. Three of them have moved on (2 in the just the last 3 years), and though it does not hurt the same, not a day goes by where I do not think about them. I feel blessed that each one had found me and fortunate to be able to take them in and provide a loving home.
I am in the process of reading this book
http://www.amazon.com/The-Loss-Pet-W...+Loss+Of+A+Pet as I have a 15 year old Cocker Spaniel who has been under treatment for cancer for the past 2 years. On 9/20 he is supposed to go back in for surgery to remove another Mass Cell Tumor. It should be fairly routine but at 15 nothing is routine.
Hope it helps for you to see that you are not alone.
Greg