Erasing the dangerous thoughts is the hardest part and what I wish I had better methods for.

Finally an opportunity to use my Dark Arts for the benefit of humanity. Here it goes:

• You see the abusive mentality of your girlfriend as an illness, and your support as a cure. Your urge to stay is rationalized as a hypothesis that being there, exposing yourself to the abuse, somehow cures the illness. Now let's ignore the fact that it is you and your girlfriend for a moment, and ask a general question: Do you really believe, as a general rule, that the best way to cure abusive people is to give them a supply of victims? Is there any psychological pubblication suggesting that this could be true? If you were a psychologist, would you recommend this as a therapy? Because as far as I know, it is exactly the opposite: enabling harmful behavior, protecting people from natural consequences of their actions, makes it more difficult to heal. That means, your staying in the relationship actually makes your girlfriend's illness worse.

• Returning to your specific case, is it your personal experience that the longer you are with your girlfriend, the less abusive she gets? (Something like: at the beginning, she was threatening to cause you serious bodily harm every day, now she barely does it once in a month.) Do you have any data to support the hypothesis that your "healing" actually works? Or is it all just imagination and wishful thinking?

• Does your girlfriend take a therapy? If you believe she is ill, she definitely should. Using your analogy, if she had cancer, would you let her stay home avoiding the doctors and try to heal her using your power of love? What would be your opinion about someone who did exactly that? Because that's what you are doing right now.

• If this wasn't a situation between you and your girlfriend, but e.g. your (male) friend you deeply care about and his abusive girlfriend, would you recommend your friend to stay in the relationship? Imagine that the friend is not dating her yet; he just noticed her a he likes her, but you already know that she is an abusive person. Would you recommend your friend to start dating her, knowing that this will happen afterwards, or would you try to stop him?

• Imagine a parallel reality where you live with a girlfriend who is not abusive. Would you break up with her only to be able to start dating an abusive girl and have a tiny chance to heal her by your suffering... because doing that would feel more altruistic, so you are morally required to choose that instead of happiness with a non-abusive girl? I am not just talking hypothetically here; the non-abusive girlfriend actually exists in your future, and it is your choice whether you open yourself for the relationship with her, or if you dump her in favor of the abusive girl you have now.

• Imagine that you stay with your girlfriend and she remains exactly the same, or keeps getting worse. (Which is quite likely: the best predictor of a person's behavior is their past behavior.) Imagine yourself ten years later, twenty years later, having dealt with the abuse all the time. Ask your 50-years old future you, who is probably too emotionaly broken to rescue themselves, if they could use a time machine and send a message back to the past, to your current self, what would that message say?

• Do you want to have children one day? If yes, do you want your children to have an abusive mother? Do you want to see them abused in the same way you are, or worse? Because they will be more helpless than you are. And unlike you, they didn't choose this voluntarily. Please realize that if that happens, it may become impossible to do help those children in any way, because in the case of divorce, the judge will most likely let the mother keep the children, regardless of her personality. (Read some stories in "men's rights" debates to get an idea about how horribly family court can work in real life.)

• Do you believe that decent human beings should help each other and support each other, as much as possible, especially when they are in a relationship? How does your girlfriend fulfill these criteria? Or do you perhaps believe that moral duties apply only on a few selected people (such as you) and don't apply to other people (such as your girlfriend)? That would mean you don't even consider her a member of the same "moral species".

• If helping other people is a high priority in your life, is staying with your current girlfriend really generating maximum good? Imagine that you would find another girlfriend, who is not abusive, who would make you happy, which would probably make you more productive. Then you could together sometimes volunteer in a kitchen for poor people, or contribute some money to effective altruist causes. Wouldn't that generate more good?

For best outcome, please read this list repeatedly, focusing on the parts than resonated with you.