New here and already have a girlfriend

I'm not in a relationship so take my advice with a grain of salt, but if you're serious about quitting and improving your relationship: talk to your partner. Explain what you're going through and how they can help, make it clear that it will take some time and won't be a straight line to success and recovery. It may be hard but hiding this away will only increase the feeling of shame and guilt. If they stay and support you, they will begin to see the improvements themselves as you recover.

But yeah, I would say definitely talk about it and be honest, it will be better in the long run.