Changey - your intelligence & self-awareness is pouring out of this update post.
Why waste all that on this CF?!
The diary thing is ... well it would be laughable if it was not so sinister & sad. It's the kind of pre-planning & self-preservation people undertake when they have a really toxic boss. And as you rightly observe - you feel like her PA.
PP have given you some great advice & resources.
when you are ready, you will deploy these, & your problem will go away. Because you know, & we know, that CF will not remain friends with you when she can no longer exploit you. So that's the short-term solution.
However ... it's not really about this 'friend', is it? It's about you, & whatever went on in your background to allow you to finally end up in such a pickle that this bloody woman is pushing you to a breakdown. May I gently suggest that, if you invested HALF the energy & time you currently put into 'managing' your relationship with your CF into therapy, within a year or so you will be so far from the broken woman posting here that you will barely recognise yourself?
PP was right in describing your 'friendship' as an abusive relationship.
Look at in in those terms. If CF were a man, & your romantic partner, we would all be screaming "run for the hills!" because she is a coercive controller.
Please - please, spend a bit of time thinking about this. Because that is a FACT.
Do you know what is not a fact? "I know I am weak". Reading that made me tear up for you. You are not weak. People who endure & survive abusive relationships ARE NOT WEAK. They are stonkingly strong. They are managing appalling, secret & hidden maelstroms of emotion, dealing with the mindfuckery of coercive control, DARVO, managing, facilitating, appeasing & pacifying their abuser, keeping the lights on & the show on the road in thir own work & personal lives, & presenting a 'all is well' facade to the world. That takes huge reserves of resilience, courage, & determination.
The thing is - all that energy & sheer willpower & creative ways of surviving - is being WASTED as it is all focused on the abuser.
What would happen if you removed the focus from your abuser, & gave all that to yourself instead? How much energy, willpower, creativity, & just general fin & happiness would that release for you?
Seek out a therapist who is experienced in helping survivors of coercive control &/or victoms of e.g. narcissistic abuse. I'm not 'diagnosing' your CF as a narcissist btw, & frankly I don't give a shit what her problem is - but you need a framework from where you can begin to understand that your CF does not function like reasonable people do - she is wired differently - so responding to her or trying to deal with her from the perspective of a reasonable person will never work.
www.healthyplace.com/personality-disorders/malignant-self-love/surviving-the-narcissist
How you choose to deal with this, & the timeframe you give yourself to do so it entirely up to you.
You posted on AIBU so will be getting some robust responses
- but ignore anyone scolding you for your predicament, or affecting disbelief that you have been unable to "just say no" - any PP beating you up with that is confusing "simple" with "easy".
Of course it is simple! I'd love to ring your CF up & tell her to fuck off & leave you alone forever. But that's not the solution. The solution is that - when you are ready - YOU will do that. You won't do it in the way I might, because you are you (& I probably have at least 2 or 3 decades experience & practice which you are yet to have ...) & you need to take on board the advice PP have given you, read some of the resources linked here, let it settle, & come to the way of dealing with your CF that feels right to YOU.
So I'm not going to tell you what to do right now.
You have had enough of that from the CF.
The most important thing btw isn;t getting her fucked off to the far side of fuck. It's getting YOU to a place where you are aboe to tell her to fuck off (however politely you might phrase it) AND FEEL GREAT ABOUT DOING SO.
That's gonna take a little work, but it's a no-brainer innit.
Hmmmm ... what will I choose ... a nervous breakdown while remianing under the yoke of my tyrant ... or a newly confident me, who has worked on whatever trauma or issues caused me to fall under my CF's spell, & who can now confidently navigate my life without falling victim again?