Awww, Liz, I'm sooooo sorry.
It breaks my heart to hear that things can't be fixed to make your buddie better.
When we accept the awesome, terrible responsibility to care for an animal part of that responsibility is making the decision to end their suffering if necessary. As my vet said, it's one of the worst parts of owning (or being owned by) an animal, but it's also the most important part.
Predinsone might help Roe's breathing, but it's also going to make him hungrier and thirstier -- and need to potty more often. Hopefully you'll be able to manage that need without too much trauma to either of you.
I'm holding you both tightly in my prayers as you begin the process of saying good-bye. Hang on to the sweet memories you have of your travels together. They'll help sustain you in the days & weeks to come ...
Hugs ...
Laura -- and Jed