Hi there. I think you know what you need to do, Hence you being on here. That’s good! At least you’ve recognised that you have a problem, that’s the first step in doing something to try to change it.
You said “in the pub after a bad day at work.” Maybe you need to find healthier ways of tackling when you’re feeling crap. Cocaine is a quick fix that in the long run makes you end up feeling worse.
I’d talk to your gf about stopping. Tbh if she won’t get onboard with you i’d seriously think about maybe ending it. Your health should be your number one priority and if she is using, the chances of you being able to just stop are slim due to the mental pull of the drug. Good luck!!