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

So, I spent seven years working at the same company.
I started out as an admin assistant and over time worked my way up to become the administrative coordinator.
My best mate, Emily, joined the company two years after me, thanks to my recommendation.
I trained her up, showed her the ropes, explained all the systems, gave her useful contacts, and even covered for her mistakes at the beginning to keep her from getting the sack.
We had lunch together every day, headed out for drinks on Fridays, and honestly, I trusted her more than anyone else.
About six months ago, they announced there was going to be an opening for a managers position.
My boss told me I was one of the top contenders.
I started coming in early, staying late, and taking on extra responsibilities to prove myself.
Emily kept telling me, That job is yours, you deserve it. I shared everything with hereven my ideas and plans for the internal interview.
But on the day of the interview, she showed up as well.
She hadnt breathed a word to me about it before.
I found out when I saw her sitting outside the managers office, waiting her turn.
She just looked at me and said, I decided to give it a go. I tried to shrug it off and not think the worst.
A week later, they announced the resultshe got the manager role.
I just sat at my desk, staring at my screen, completely numb.
After that, things started to feel off.
As the new manager, she began changing procedures Id put in place, removed me from certain tasks, and made me do these pointless reports.
One of our colleagues told me shed said I didnt have leadership skills, and that a lot of the ideas shed pitched as her own were actually things Id shared with her in confidence.
One afternoon, I confronted her over coffee: Why did you say those things about me? She replied, Its just business, not friendship.
I had to secure the position for myself. I reminded her of all the things Id done to support her, but she just shot back, That was your decision.
I never asked you to.
Since then, the atmosphere at work has just become unbearable.
She speaks to me coldly, corrects me in front of everyone, and gives me meaningless tasks.
I go home in tears, anxious, and dreading work to the point where all I want to do is quit.
At the same time, it really gets to methe thought of leaving without saying my piece.
Now Im stuck at a crossroads: do I just grit my teeth and keep quiet to avoid being out of a job, or do I leave and start over somewhere new?
What would you dowould you stay, or would you walk away?