This one hits close to home. One of my prior attempts at sobriety ended like that as well. I was underestimating the pressure certain social situations were creating. And the part where one is watching how many drinks the other people have and "adjusting" to it while not being entierly satisfied...I did that too, and felt similar guilt and sadness afterwards.
But unlike you, I continued drinking for a year and it took me mentally to quite horrible places. Kudos to you for being assertive and going back to your support system so quickly. Ok, so the occasion arose and you drank-it was just too much of a drinking setting too soon, but you got back in the saddle. Now that you had this experience, you know for sure. Don't beat yourself up and don't be too anxious about situations to come. Eventually, in this process, there will be a time when social situations are becomig less threathening. Less threathening yes, but atleast for me, never harmless.
Most of the time I just tell the people I am with that I am not drinking any alcohol anymore, as a protective measure.
What one can really feel from your post is your willingness to commit to sobriety and to reach out for help. You have a good attitude about what happened and I am sure you will succeed. But please give yourself some time to recover- it takes time and the "head not shutting up part" is something many people experience early in recovery and that gets better. Good luck Jo and all the best,
S.