Your situation sounds a lot like 3 of my previous relationships. The only difference is you still have your gf in your life whereas all mine left me after two drinking occasions much like yours. Three relationships later and a lot of depression and loneliness, I finally checked myself into Daytox and attend AA because I know I will not have a successful relationship with booze involved.
Pick yourself up from this and learn from it. Be grateful that you still have someone like your gf in your life who sounds forgiving and supportive. Don't lose her over alcohol like I did mine, I know from experience, you will regret it and you will have a very difficult time forgiving yourself and moving on.
Best wishes