The disease of alcoholism takes over us and will do anything to protect itself-- it convinces us to lie, cheat, deny... to ourselves and others. It will do whatever it it needs to do to keep getting alcohol.
I just heard my dad tell my mom he only had 2 drinks when I had seen him have 3 with my own eyes, and I suspect he had more than I saw. This really surprised and hurt me because it's one of those things where kids (even adult kids of any age) automatically think their parents are infallible and trustworthy, only to find out that they are capable of bold-faced lying! I thought about WHY he lies about how much he drinks-- to keep the facade going, to act like he doesn't have a problem and/or has it all together, to keep people off his back, to even lie to himself about how much of a problem it is or could be-- all so that he can keep drinking. The end result is to keep drinking.
Then I thought about things I have done in the past-- sneak drinks, lie to myself and others about my problem, play off the amount I've had to drink-- and I realized that it is just what alcohol does to those of us who have a problem with it. But we are stronger than that and we don't have to give in to that alcoholic part of us. I am convinced it is not the real and true us, that we have to separate ourselves from it and live honestly and in sobriety.
All you can do is keep on this current path, not even for your girlfriend's sake or the sake of the relationship, but for your own sake. You cannot save your relationship or be there for anyone else if you don't save yourself from yourself. Best wishes.