I don't want to say should or shouldn't, that is totally your call man. You've had that puppy forever. I've got a 2yr. old American Eskimo and it kills to think of him in your Sheltie's state. If Clinton was in that kind of pain I would choose to put him down. It would b selfish for me to keep him alive. His life biographically is over... its the biological part that's still kicking. It would be my fear of loss that'd keep him with me. I'd have to cope and do what is, in my opinion, in the best interests of the dog. But I understand the opposing argument too: killing animals is wrong, you want to appreciate their last days--I totally respect it. Whatever you decide don't let anyone tell you it was the wrong one... you know what's best for your dog. Hard decision man, I'm sorry. What's his name?