I understand it and sympathize. I don't think there's anything wrong with him riding. When my dh can't "fix" what's wrong he goes for a really long run, situps, pushups, weights, etc. Works out all of his frustration and feels better after. I understand the pull to do both...take care of your little fur baby and just go hit something as hard as he can (in this case, a good mountain trail). Good luck with all of your decisions and big hugs about Maggie. I really do continue to hope for the best.