Perhaps some folks will think you're no longer part of the "Cool Crowd". And rarely has the "cool crowd" from my younger days amounted to anything close to their potential!
Perhaps the same folks will be somewhat frightened of how their own drunk behavior will be seen by someone not under the influence? Ever show up to a party late and everyone is 3 sheets to the wind? A crowd of idiotic bores!
"You're not drinking?"
"Doctors orders... I'm on a prescription (sobriety) for an illness (alcohol abuse/dependence.)"
No one has the right to inquire what's 'wrong' with you. Just because they ask, does not require an answer.
My doctor, upon hearing how much I drank, said my blood tests look fine and my liver is not enlarged, but I should "reduce the chronicity" of my alcohol intake... to a glass or none a day! One or two glasses?!?!? Then why bother at all (not to mention that I can't really stop at one regardless.)
You'll do fine, just stick to your principles and decision. Congrats!