Susan, I have to admit to shedding a tear or two myself when reading your post.
I have great empathy with you, I too had to make that terrible decision four years ago with my Lakeland Terrier. He had suffered with Colitis for over twelve months and there came a time when his quality of life was starting to be affected.
The decision was a tough one for I loved Corky dearly, I wanted him to live forever, but I also new I could not allow myself to let Corky live in pain.
We had such memorable times together, but time does heal and now we have Buster who is just adorable.
Whatever you do, please do not beat yourself up over the tough decision you had to make. I did and it took me much longer than it should have done before I felt ready to offer a new dog a loving home.
My thought are with you.
MIke.