Sorry about your loss. I know the feeling and it sucks. They look up at you with their big eyes and you have a hard time doing what you know must be done.
In my entire life the ONLY time I ever saw my dad dry was after putting down our dog of 15 years. It was on the way back from the vet and his loss of control was so profound that he nearly ended up on the curb. I'm the same way.
It truly is the one thing I hate about having pets is how short their lives our compared to us. I have 4 cats right now and they are like my children. I can't imagine not having them around but I know sooner or later it will happen, and my wife will be devastated.
Just remember that he is at rest, maybe having fun with others, waiting for you. It's easy for him to breath there, too.
I know most people have seen this before but I find it so moving I can't help but repost it:
The Rainbow Bridge Story"Just this side of Heaven is a place called The Rainbow Bridge.
When an animal dies that has been especially close to someone here, that pet goes to Rainbow Bridge. There are meadows and hills for all of our special friends so they can run and play together. There is plenty of food and water and sunshine, and our friends are warm and comfortable. All the animals who had been ill and old are restored to health and vigor, those who were hurt or maimed are made whole and strong again, just as we remember them in our dreams of days and times gone by.
The animals are happy and content, except for one small thing, they miss someone very special to them, who had to be left behind.
They all run and play together, but the day comes when one suddenly stops and looks into the distance. The bright eyes are intent, the eager body quivers. Suddenly they begin to break away from the group, flying over the green grass, their legs carrying them faster and faster. YOU have been spotted, and when you and your special friend finally meet, you cling together in joyous reunion, never to be parted again. The happy kisses rain upon your face, your hands again caress the beloved head, and you look once more into the trusting eyes of your pet, so long gone from your life but never absent from your heart.
Then you cross Rainbow Bridge together......."