Thank you for posting here, must be very tough for you right now. Sounds like Duke was a beautiful companion to you for quite a long time and it is totally understandable that you struggle with losing him. That’s always the hard bit when we love someone so much, their loss really affects us. And a lot of us in this Forum can relate to that.
Have you checked out Griefline’s resources such as https://griefline.org.au/resources/losing-a-pet/? You might find some of the coping strategies on the website helpful in dealing with your loss.
I wonder what it is you do to look after yourself during this difficult time?
Take care – I’m thinking of you in your grief.