Hi Alkaline Dragon,
I'm not sure if I'm right here, but it could be food for thought? It's possible that you are projecting your feelings towards your mother onto your girlfriend, but it feels like it is towards you gf that you feel this anger. We tend to project our parental issues onto our loved ones at a certain age...usually late twenties to mid thirties. Women do it with their unresolved father issues and men do it with their mother issues.
It might be that expressing your anger towards your mother TO your mother (putting the blame where it belongs) might help you resolve this, or at least get it off your chest, so you are no longer carrying it around?
What do you think? I know it's a scary thing to think about doing, and maybe you aren't ready to have it out wiht her yet? It might help to speak to a therapist about this if you have one?