Daniel,
I don't have a lot of experience being sober, but I have a lot of experience with that thought that quitting will kill you and continuing to drink will do the same. I've tried a lot of things, but the most recent and maybe best thing I did was to go to the doctor and fess up. She was very understanding and prescribed medication that truly helps. It's only been 5 days, but each day I feel better than the one before. I did start tapering before I went, so that I was at half my usual consumption and that probably helped as well. Though it made for some uncomfortable days in the meantime, it wasn't unbearable.
I think if you tell your girlfriend that you have a problem AND you have made plans for addressing it, she will most likely be supportive. She may know more than you think she does. But of course, that's up to you.
Hope this helps some.