Marie, I fell off just a few days ago, and am back on track Day 6.
It'll take a day or two to shake off the shame; about as long as it takes to clear your head.
Then it takes fully accepting an idea that was new to me when I first started nosing around here-- LOTS of people make "false starts." Before really trying to stop, I had the idea that most people have early success; quite the opposite.
Once your head clears, go back to the semi-conscious moment when you made the decision to take the first drink. Did you have to go buy something? Was it at a party?
Now try to learn from that moment. How could you have avoided it? What thought process is missing from your arsenal, that could have helped at that moment?
Bowing out of social obligations for a few days, or a few weeks, could be a good idea. Last night I absolutely forced myself to stay home; wrote bills during "party time," then watched Netflix "Orange is the new Black" until 3am. No booze at home (this requires your husband's cooperation).
I'm a 56yo father of two 12yo twin boys. Maybe this is why I related to your story so strikingly when I opened it first this Sunday morning in Germany.
You will beat the negative thoughts. Then learn from this slip, and start building again. You're just one dry night away from being able to look back on a fresh start.