I know exactly how you feel mate
I lost my best mate "Buddy" two weeks ago after having him from a pup for 16 years. A man couldn't have wished for a better dog and he died in my arms. I must admit I cried like a baby and two weeks later I still expect him to come through the door. He was healthy right up to the day before he died, never had a days illness in his quite long life, but his heart gave up on him. One small blessing is that I never had to watch him suffer. I still have his ashes on the mantle and when I'm up to it I'll scatter them around the backyard. The problem is you can never really prepare yourself for the loss of a dog. Even though he was 16 he'd still go for a walk every day, chase a ball around, I can't believe he's gone.
My comiserations, I know the pain the loss of a good dog causes.