What do you think about me scaring myself with the way that I cope?
How are you coping?
I'm physically hurting or abusing my girlfriend
Hurting someone else to ease your pain will only land you in jail. Learn new coping mechanics that don't harm other people and consider talking to a doctor about your abuse. Make sure you apologize and explain to your girlfriend what is going on with you.
I don't always hurt her, it's just when times get tough I have to vent my anger. She understands what I'm going through and we talk it out.
It doesn't matter if she "understands" because most likely that isn't understanding, but rather fear. You need to respect your love for her and let her go, or else stop abusing her entirely.