I'm with Anna, you don't owe anyone an explanation. The only person you have to be true to is yourself. I personally would be cautious about sharing with your work collegues. Work is work, keep it seperate from your personal life. They don't need to know. But that is just me.
If someone asks you why you aren't drinking say "why would you ask me that?". Now they are on the spot. It's fun to watch some people stumble for an answer! Works for a variety of question people ask
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