I can't offer much else in terms of the accident, because you've gotten right on target advice here.
I might mention something about your relapse though.
I'm truly baffeled as to what happened - how I could do that again. How has it come to this?
I think it is
so important not to leave a relapse behind you without thinking deeply about exactly why you relapsed.
If you don't learn
why you relapsed, you will simply repeat that behavior again.
"No one else knowing" suggests you might be seeing your journey of recovery as a process of external pressure on you: that it is about satisfying other people's opinions or control over you, instead of a very internal process where YOU knowing about your drinking is the most important thing.
It also sounds like you are attaching more importance to the danger of driving after you drink than to the danger of taking that first drink.
But, if you think about it, taking that first drink could have led you to any number of dangerous situations: a bad fall, a suicide attempt, alcohol poisoning. The list goes on.