Sadly, I think it's time. Both of my loves, one 12 yrs old and one 15, spent their final hours being held and loved in their home. When we realized there was no hope and that our dogs seemed to no longer enjoy life and/or were suffering, we asked to have them put down at home. I couldn't bear to let it be done in an unfamiliar place.
It was hard, and even now, a year and a half later, I still grieve as I write this. It took several years with my second dog before I started getting attached again. I think, right now, you need to make the decision to let go for your pup's sake. What has helped me is the belief that they do go to heaven and they too meet up with those they loved. I know the pain to you can't be avoided but I will say a prayer that it be eased for you.