TuckerVA,
I know it is impossible to know how you feel because my situation was a different from yours, but I do know what it is like to love a dog at a level most people cannot understand.
I had to make the painful decision to send my beloved companion Alex to the Rainbow Bridge 2 years ago. Mentally and physically he had deteriorated to the point where he had very little quality of life. However, when he looked up at me with those sad eyes it made it so hard to do what I knew was best for him. I know in my case I was selfish and put the decision off for several weeks longer than I should have.
One thing that made the process easier was I had someone come out to the house to do the actual euthanasia. I was able to hold Alex during the process so he was calm and relaxed, and we got to spend our final moments together. I cried for days afterward, but looking back I know I did the best thing for him. Sometimes doing the best thing for your pet isn't necessarily the best thing for you at the time. However, when you look back at it you'll know you made the right decision.
My prayers are with you during this difficult time. It really takes someone who has gone through this themselves to know the feelings you are experiencing. Whatever the outcome is, my thoughts are with you and Tucker.