N, Be careful working out there in the heat and humidity. I hope that you are drinking plenty of water. The same applies to your dog...
It's okay to have moments such as you had this morning. We all go through it at some point. It could be trimming hedges, painting or mulching flower beds. It could be a movie, music or a special place that you both went to. Cherish those memories and allow them to wrap themselves around you. The sadness will decrease as time marches on.
Take care of yourself and your pup.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.