The question with no answer. I faced it twice. When you cry until you can't cry anymore. When it hurts so much to watch them fall down and not be able to get up. When the only time they are at peace is when they are sleeping. When they don't want to be petted or held or comforted. When you see fear and pain in their eyes. When they try so hard but cannot control their bodily functions. When you know there is no getting better. Then you still won't know for sure. So you just do the best that you can and understand that you can err on the side of waiting too long as well as acting too soon. You are the one who loves this being and you are the one who has to decide what is best. They wouldn't want it any other way. A decision made with love is the last gift that you have to give. And as the AntiPam said, you will have the doubts afterward. Please take care of yourself. I know how difficult and stressful these days are for you.