I suppose it depends how close you are to your gf and how long term the relationship is as to how much you disclose.that said, I would not advise pretending to drink.I'd say Iwasn't drinking,just not sure how much detail I'd go into.
With your mother, be wary as many mothers do not want to acknowledge their children have a 'problem' Mine said 'oh you're not THAT bad' -cue excuse to carry on drinking
I just tell people I don't drink anymore.