You took care of your companion as best you could. What you did took courage beyond what a lot of us can muster.
I am quickly reminded of the story Roy Huntington, editor of American Handgunner, told of his own experience with putting down a beloved pet. That story appeared in his "Insider" column and can be found here: On responsibility: Ginger's legacy — a true story - The Insider | American Handgunner | Find Articles Re-reading that for umpteenth time got my eyes misty all over again.
Be prepared for an onslaught of comments that what you did was cruel and inhumane, why didn't you take Frisco to the vet to put him down, and similar blather, but those will come from people who don't know you and don't have the same level of commitment and personal responsibility toward their companions that you do.
You're an honorable man, and surely worthy of Frisco's devotion. May God ease your sorrow.