I've thoroughly read all that so here's my input. Obviously it's my own perspective. However. It will be blunt. As you said you are a blunt person, I assume you can take it. Decide if you want to read on with that in mind.

That was the disclaimer.

She is like this with you and not with others, because you are close to her so she "lets go" in private and shows her bad side without restraint.

This is NOT your fault. It's simply part of who she is now. Do not let yourself get guilt tripped over this.

At the MINIMUM, she needs to learn management of her dysregulated emotions, no matter what the original reason is for the dysregulation. That's her responsibility, not yours. She has to work on that on her own/with professional help, not with you.

She may be able to change her hostile worldview to a more positive one, but you will NOT be able to fix it for her. AGAIN, it's HER responsibility, not yours.

I understand there were those initial intense emotions bonding you to her this strongly, but if this goes on like this, you may also develop abandonment trauma yourself. Perhaps worth looking up trauma bond, too.

I say that because, it must feel like a lot of stress and burden to have to keep feeling like your heart is being broken having lost her, that you constantly have the one person you really feel in love with getting angry at you, and that she doesn't seem to be this angry and annoyed with other people.

So because of that, I can understand why you have such a strong drive to try and fix all this. But you can't fix her or the relationship on your own. You shouldn't even try. You should not try and dig into her "core issue" whatever that may be. Not your responsibility, it is not appropriate for the relationship, and you do not have the qualifications and deep knowledge base or experience for it.

So, either therapy and/or some other kind of professional help for her, maybe some skills learning for you too, and/or couples counselling, probably of the kind where the partners first have to establish a foundation working on themselves (with help from the counselling) separately before working together on the relationship as a team.

As she is now, she's not ready for a working relationship. I don't know your relationship history, so I can only talk about her here.

And what causes the problems: I wouldn't know from this much information.

It could be any or all of these things, or any other things not mentioned here:

- trauma like you said
- too much stress in life
- incompatibility between you two
- or, it's simply who she is.

Finally, my advice: focus on YOURSELF, your own feelings, as it right now seems like, you keep focusing on her feelings a lot and that will just lead to a disaster too if it goes on like this. Your own feelings will end up being too much if you haven't managed to "fix the problem" in time with this "fix it" approach, if you continue like this, then unfortunately, I guarantee this disastrous ending for you.

I hope some of this helped.

PS: A book you might like on handling conflict in relationships that keep going bad: The Science of Trust: Emotional Attunement for Couples by Gottman.