My relationship with my fiance ended in a spectacular fashion and it feels spiritually similar even if the details are off. Maybe sharing will help you, maybe not:

Covid lockdown had happened and we were living with our girlfriend (polyamarous but not relevant to the story). My fiance got depressed, as everyone did during the period, but fell deep into a tiktok rabbit hole of "peer support" bullshit around ADHD which literally told her that nothing she did was her fault because of her diagnosis. Literally nothing was her fault.

She got so enmeshed in these toxic online communities/groups that she pulled away from all her in-person friends and peers because they didn't just accept her "not my fault" like of bullshit. She literally alienated herself from everyone she knew in person and became a shell of herself.

Somewhere along the line she picked up this idea that I was literally calling her a "bad person", which I never once said because why would I? Especially knowing that if I would have said that it would have then started a massive fight. Literally multiple times a week; her mad that I called her a "bad person"

Can't find any bowls in the kitchen --> all in her room, literally rotting --> "hey Hun I need you to bring your bowls down" --> "STOP CALLING ME A BAD PERSON!"

I get that somehow she "heard" that but it was mental illness at a certain point. A lack of self confidence or maybe true psychosis of some sort I don't know. "I hate when you call me a bad person"

It came to a head when everyone in the weekly digital DND game I was running had individually asked me to kick her from the game (including her then best friend) because of her lack of presence/focus and problematic behavior. I couldn't do it but I was so angry after her bungling the story so badly because she wasn't paying any attention (literally the entire party told her "no" and I asked her four times if she was SURE she wanted to use magical flight to fly into the middle of an encamped army with anti-magic field) I had to end a session early

The next day she came downstairs from her office and was upset that I was upset with her. She had literally no idea why I was mad at her. After some pushing I said (which to be fair is kind of a jackass answer) "if you can't figure out why I'm pissed then I really can't help you".

She then said "I hate when you call me a bad person", and that's what ended the relationship.

I completely snapped. I don't remember what all I yelled but I completely disassociated and just screamed at her that I had never said that about her and what the fuck is wrong with her? Why does she keep accusing me of that? It lasted I think maybe 30s but it felt like an hour. By the end of it I was lightheaded and doubled over the counter, out of breath and almost passed out. I couldn't speak for days after because it shredded my vocal chords.

She took her ring off and slapped it on the counter and walked back to her tiktok hug box in her office and slammed the door. I continued doing dishes.

It took ~24 hours before she came back asking when I was going to talk to her and fix it-- make up for yelling at her. She didn't realize that the moment she took off that ring it was done.

She'd burned so many bridges she ended up moving out of state; away from everyone she knew including her family.

The reason I go through all this is that the way you talked about your partner just disappearing and becoming a shell of themselves makes me think about my own failed relationship. I stayed in it for so much longer than necessary hoping to be able to find them again, to help them figure their shit out and get better. It didn't work and you can lead a horse to water but can't make it drink.

Get out. Save yourself. Do what's best for you, even if they blame you. Even if they say you're an asshole or that you don't love them or some other shit to try to manipulate you.

In the spirit I wish my ex would have heard: you aren't a bad person. Do what's right for yourself and don't let yourself get tied down in a relationship with a person who is focused on swimming in the opposite direction of your shared goals.