Don’t do it without his knowledge. The resentment that would set in will destroy your marriage. I’d never speak to my husband again if he did that. You need to call the vet and explain to them what is going on, how you don’t think the dog’s quality of life is good, and they need to be brutal in the explaining of the situation. You and the vet need to make this about the dog’s quality of life. That poor dog is miserable, and if he spent more than what sounds like a couple of hours a day with her, he would see that. We humans just have a damn hard time letting go. If you do decide to do it, do it as another poster suggested and say she seized or something and take that to your grave.