I am really sorry for you, but you are making the right decision, as I'm sure you already know. As far as your Belgian shepherd is concerned, I'm sure it won't be easy for her, but she will cope. A few years ago I had my older terrier put to sleep, and was left with her daughter, who had never been wthout her mother before. She got used to being alone quite quickly - I think she realised that her mother had been ill. It will be quick for your Lab, and it is the best thing you can do for him. I hope tomorrow is not too hard for you.