I know how sad and afraid you are. I just went through this with my beloved Hooch who died of kidney failure. I had a bit more time to become used to the idea of losing him than you do, but when he got sick toward the end it happened very fast. You will never be ready to part with him and your heart will stay broken for some time. I've lost other wonderful friends and while I still miss them terribly, the raw hurt is gone and I'm so thankful I had the time with them. I loved Hooch more than any dog I'd ever had. He came as an emaciated, dying dog from the animal shelter so he needed care from the start. I cry a bit everyday (we lost him mid-February) but when I look at his picture I smile. Cry. Be angry. Love your baby. Say goodbye and farewell. When the time comes, be brave and hold his paw. Tell him you love him and let him go. You will get through this. Grieve. Be sad. Smile and remember. My thoughts are with you. The feeling will never go away but the raw sadness will, in time, be replaced with happier memories of when times were good. Be so thankful you had him for twelve years.