Fur babies really do become family, and even more, for so many of us. They're ALWAYS there for us. I know how you're feeling. I've been through it several times; especially recently, with a darling rabbit that we rescued.
He will always have a place in your heart, and I know he had a great life with you!.
The marker is beautiful. The care you've taken with remembering him and giving him a thoughtful burial shows how much you loved him. He was a cute dog!