I have a hard time believing you let him down, Too. My dad passed when I was quite young, and if I kept a list of things I have done/not done that would have let him down, I wouldn't have had the time to drink--I would have been inking that list.
I would bet you're a great mom, good friend, and a daughter that he would be extremely proud of today for your year of sobriety.
It's easy to think of how we would disappoint--but harder to think of how proud they would be of us--I'll bet if I asked my dad to check with yours quick--he'd say he was damn proud.