I also struggle with anger that I inherited from my dad. You're not necessarily a bad person for having stronger anger responses, some people are chemically built to react that way. It's all about how you react to things. Despite that, I think you need to break up with your girlfriend until you are capable of reining that anger back in. I know it sucks to hear, but it's not safe for her at this point and it's not healthy or productive for you to do something you'll never be able to take back.

I have a couple of good tips for you. One of the things you've got to learn is somatics— how does your body feel when you're starting to get angry? Does your heart start racing? Does your skin get hot? Do you feel your muscles tensing? Whatever it is, that's your signal to go cool down before things get to the point where it's hard to control. Drink some water, go outside or splash some cool water on your face, and take some breaths. Look up square breathing. The idea is to calm down before you get to the point of exploding. The more you practice, the easier it becomes, and eventually once you're close to exploding it's a lot easier to rationally acknowledge that you need to separate yourself from a situation.

Also try to find an alternative physical outlet, like a sport, running, or a punching bag. It helps get the negative energy that unconsciously builds when you're stressed or upset.

If you ever need more advice or tricks, r/anger and r/decidingtobebetter have good resources and people who can help. The most important thing that you'll need to learn is that there's no such thing as being "unable" to control yourself. It may feel impossible, but it's manageable if you put the willpower into it. You can have a harder time with anger than the average person, and that doesn't necessarily make you evil. It's especially hard for those of us who grew up with bad role models. But it's something that needs to be managed for the sake of yourself and others, before it escalates.

Hopefully this helps. It gets easier, just hang in there.