I am so sorry Archie was so sick and could not get better in spite of all the wonderful care you gave him over his many years.
Your update was very moving and while it was a heartbreaking decision for you to allow him to move on, it was one made because you loved him. Millie must have known it was his time too.
Millie had a wonderful bond with him ❤❤as did you, so I know you will be a comfort to each other as you both process the loss of your beloved boy.
Sending tons of gentle hugs to you and Millie, and positive vibes for Millie's vet exam.