Hi Amanda,
I have eight years of sobriety as well and when you don't think about
not drinking all the time, then there are those thoughts of, 'well, I have this licked.....' that can pop up and quietly settle. I have to just poke myself to think through the 'just one drink'.
Try not to berate yourself too much for the slip, worrying about the past can lead to a vicious cycle of regret, making it harder to pull yourself free.
Learn from the mistake and take this lesson with you going forward. You are human after all.
You know how well you can do and now you have this bit of a slip to add to your arsenal.