I Worked at the Same Company for Seven Years: From Starting as an Assistant to Becoming Administrative Department Coordinator

So, I worked at the same company for seven years.
I started off as an assistant and eventually worked my way up to be the coordinator for the admin department.
My best friend joined the company two years after meactually, it was because I recommended her for the position.
I trained her myself, taught her the ins and outs of the system, gave her contacts, and honestly, I even covered up some of her mistakes at first so she wouldnt get let go.
We always had lunch together, went out on Friday nights, and I trusted her more than anyone.
About six months ago, a managerial position was announced.
My manager told me I was one of the top candidates.
So, I started coming in earlier, staying late, picking up extra responsibilities.
Throughout all this, my friend kept saying, This job is yours.
Youve earned it. I shared everything with hereven my ideas and strategies for the internal interview.
On the day of the interview, she showed up too.
She hadnt mentioned anything to me beforehand, so I only found out when I saw her waiting outside the bosss office.
She just looked at me and said, I decided to give it a go. I tried not to think badly of her.
A week later, they announced the resultshe was chosen as the manager.
I just sat at my desk staring at my computer, completely numb.
After that, things started to feel odd.
As the new boss, she started changing the very processes Id put in place.
She removed me from certain tasks, asked me for unnecessary reports.
One of our colleagues even told me that shed said I didnt have any real leadership skills, not to mention shed presented several of my ideas as her ownthings Id shared with her before.
One afternoon, I asked her straight out at the café: Why did you say that about me? She said, This is work, not friendship.
I had to secure the job. I reminded her of everything Id done to help her; she replied, That was your decision.
No one made you.
Since then, the atmosphere has been unbearable.
She talks to me coldly, corrects me in front of everyone, and assigns me pointless tasks.
I come home in tears, anxious, wanting to quit.
At the same time, Im so angry Id have to leave without saying my piece.
Now, Im honestly at a crossroads: either I keep my head down and put up with it just to keep my job, or I stand my ground and walk away, starting over from scratch.
What would you dowould you stay or would you leave?