Oh, wow. That just hurts my heart. I was so happy when you rescued Dewey from his loneliness and even happier when you and Bryan turned out to be fantastic parronts.
All I can say is that Dewey was very lucky to find you two. He likely had some health issues (unfortunately, pet shop birds often do), but you guys gave him a real home and human flock that loved him dearly.
I am so sorry for your loss.