Oh Baz, my heart goes out to you. I have a little special needs cockatiel and I can't imagine being with out him.
You may feel bad for having to put your little one down but I'm sure he was thinking you were wonderful for being there in his last moments and taking away his pain. There was really nothing more you could do. Take care, the best you can do in this situation to make good out of it, is to get the message out there and warn others about the potential dangers of leaving an animal out side without suporvision. I know that doesn't make you feel any better about the hole situation but if it saves one other bird or mammal, that's what counts. There is always a reason for everything. As for you not crying, be careful man, you may still be in shock. I was like that when I lost my uncle and when it came it was real bad. Take care of yourself and get those feeling out.