I'm so sorry.

I know your heart must be breaking. There's nothing like this kind of grief, and a lot of people just don't understand, so I'm glad you found this site.
What is your retriever's name? If you can, let yourself take comfort in knowing that he is now in a realm where he'll never experience any kind of pain. His spirit is experiencing only bliss, and he's not aware of the pain of separation from you.
Another thing: One of the universal symptoms of grief is guilt. So if you feel guilty about anything you did or didn't do for your baby, please know that this is normal. We're all "only human" and we can't be perfect. All that matters is our love. Your precious retriever knows this, and you and he will be reunited eventually.

In the meantime, you don't have to worry about him.
Please let us know how you are doing.
My sincere sympathies,
Love,
Kathy