Yeah, from what little I've read from your post and comments it sounds like stuff I've dealt with before. Certain people, when faced with situations like this, shift into "I'm being wronged, time to deflect blame and attack" mode, and once they're there it never descelates until well after you've separated from them entirely.
If they do something hurtful to themselves or make a mistake, it's your fault and you're horrible. If you feel hurt by them or make a mistake, it's also your fault and you're horrible. You can say things that are totally innocuous, and they'll find a way to call it abusive. They'll call you a gaslighter when they're the ones acting that way. They may even try to antagonize you into actually abusing them so they have real ammo that justifies their position. They'll threaten suicide and imply it's your fault.
You can take all the time in the world to try to formulate just the right words to try to help, won't work. They'll probably just get angrier. You can freeze up and say/do nothing. Doesn't work, that enrages them. And the longer it goes on, the worse it gets. It can get violent.
And it's a sad thing because you care about that person, trust that person. They're in pain and you want to alleviate it, maybe try to except your "side of tbge blame" , but you just can't. It's done.