I would say look at it for what it is, nothing more - nothing less. You drank a beer, and you had plenty of opportunity to avoid it. You could have not gone in the first place. You could have left when you realized they were serving alcohol even though you checked it out ahead of time. You could have ordered a soda or water. You could have said no thanks.
I list those not to belittle or make you feel bad, but to point out that whatever your plan was it either isn't enough or you didn't follow it. The link below is to your thread when you started out and has a very detailed list of what you planned to do moving forward. Take a look and ask yourself if it need changes or if you just need to work/follow it more closely.
Learn from it and move forward, coming here is a great step in that direction. There is no reason you cannot so this.
http://www.soberrecovery.com/forums/...-tomorrow.html