Sorry man! I am sorry for your pain, the one thing about these best friends is that the decision of thier fate rests in your hands. In my avatar is my best friend in the whole world, he just turned four yesterday, in Boxer years I am lucky if I get 4 or 5 more with him. I look at him sleeping or just being a goof ball and I think about it all the time. My only solace that conforts me that I want you to try and think about is that of all the different fates these animals can end up with, that for whatever reason you and that puppy crossed paths and formed a bond that can never be duplicated and to repay for his friendship you always made sure he was warm, you always made sure he had something to drink or eat and most of all you always made sure that he was safe. You held up your end and he held up his. If it were me I would keep him going until he started to feel any pain or discomfort. Also...I would seek a second opinion.