Your girlfriend was never going to be the reason you quit, even if she stayed. You can't quit for anyone but yourself and the only person that can keep you sober is YOU. While the break up might hurt and trigger you to drink, drinking will only make your pain worse and last longer.
It is time to just focus on yourself. The first thing you need to do is get sober. Take it one day at a time and get through the day without picking up a drink. Next, make a recovery plan. There are a bunch of recovery programs out there, there is sober recovery, and there are plenty of counselors that specialize in addiction. Utilize as many resources as you can, you CAN do this.