Sorry for you loss. Try to remember more about the fun times you had with your puppy and don't dwell on your puppy's final day.
I used to have a cat and we were both really attached to each other (often literally). He was great company and we had many enjoyable times together. He was a little over a year old when he too was run over right in front of our house. The woman living over road told us a few days later that she saw him that day trying to catch birds and he was apparently enjoying himself. Just knowing that seemed to help.
So remember the enjoyable things your puppy was doing, and hopefully, it won't hurt as much.