I am sorry for your loss. I too have put my beagle to sleep a few years ago and yes it hurts. I don't know why I torture myself and wanted another dog. Now I have a yorkie and I cry just thinking of the day this will happen but death is inevitable and you did the best for your little guy. He crossed the rainbow bridge and is now waiting for you. Cherish your memories and know that he did not suffer because of you.
http://rainbowsbridge.com/Poem.htm