Dear friend, showing your anger and frustration on a wrong person is more harmful. I meant you are using your girlfriend as a sponge to absorb your frustration. Not surprised if she leaves you as she will thing of life after marriage. Why not!!!!
Now your priority is to assess the reasons for your anger and handle that situation than focusing on Anger. You will start losing people around you and probably land up in self destructive acts.
You can surely come out of this situation if you seek help ASAP
Next Steps
Take appointment with a Counselling Psychologist in your area and work consistently to get out of the situation. life is beautiful, begin from where you can begin