The good news is that unless your girlfriend is an alcoholic too, she should appreciate getting to know the real you. I can't speak for all women, but it was more important for me that a guy care about me and be a self-sufficient, clear-headed person than it was about partying or "showing me a good time." Maybe you're underestimating your value as a person......
In any case, I found within a month of being sober that I actually had a better sense of humor and was more "present" with other people when I stopped drinking. If you watch a bunch of drunks out socializing, they only think they're more charming......
It take time for sure, but it gets easier.