Just wanted to give a quick update on this now that Byron has passed.
In retrospect (and the pain of putting him down is still fresh), I'm glad for every single day we were able to spend with him, even those days toward the end.
The past couple of months we had with him were actually not that bad. Once his skin condition cleared up, he was in better health and spirits. As the snow melted, he spent more time walking around our yard and his appetite was great.
Unfortunately, last weekend he took a turn for the worse very suddenly. He started whimpering when we would try to get him up, which he's NEVER done. It was obvious that he was sick, so we took him to the emergency vet to have his blood and urine checked (in the past, he had a bladder infection that had gone systemic, so that was our fear). It all came back normal, so at that point we feared it was neurological. He stopped whimpering, but was completely paralyzed, so at that point we assumed the worst.
On Wednesday, Byron's neurologist confirmed that his GME (auto immune disease that attacks his spinal cord) had flared up and this time we could really do nothing. He can no longer tolerate immunosuppresants, so there was literally no way to stop the infection. The whimpering was due to his spinal cord flaring up, but that section of the spinal cord quickly deteriorates, so the pain is short-lived. But with no way to stop it, the infection would have kept working its way up the spinal cord until Byron's heart stopped. We obviously did not want Byron to be in pain, so at that point we made the decision to put him down.
My husband was a mess that first day, which I expected. He's still depressed, but getting better each day. I know my husband did everything he could and even if I didn't always agree, I respect that he was doing his absolute best for Byron.
Our other newf (with osteosarcoma) is tolerating his radiation and chemotherapy very well and is seemingly pain-free and happy. I am enjoying every day with him and am praying we get as much time as possible. Putting Byron down was one of the most painful experiences of my life, I know that I could not handle putting down Bo anytime soon.
Anyway, thanks again for all of you for your insight/advice/support!