My condolences to you and your family. It’s one of the toughest things that I have ever gone though. We just lost our girl a couple of weeks ago. We still feel her presents in everything that we do, and it reminds us of how much she has impacted our lives. They are the first ones to greet us at the door and the sadest when we leave. There is lots of sorrow but also many happy memories that will live with us as long as we are still alive.
We had a lab when I was in high school that started chasing our truck when we drove out of the yard. We were stupid kids so we didn't correct the behavior right away like we should have. One day I thought he had fallen back and I was clear to accelerate away. Thump thump. He dragged himself into the ditch and I ran back to the house to get the .22 LR. Didn't even have time to be upset...I was late for work. In your situation you have a lot of time to think about it, which must make it infinitely worse. My condolences. Best advice is to get another one right away. A new puppy will wipe out a lot of sadness from just about anything, but especially the loss of a dear pet.