My coworker betrayed me

I’ve been applying for other jobs because my current workplace only offers part time hours and barely a living wage. I got an interview from a company which checks all my boxes, the interview went alright and the hiring manager asked me to provide references. Now, usually, I provide references from my previous employers. However, this time I asked one of my current coworkers if she was comfortable serving as a reference for me. And she said she’d be apparently more than happy to do so. So I provided her contact and one other contact from my previous job.

The next day, I show up to work, and this coworker tells me that she went ahead and told my manager that I’m planning to leave this job, and she basically low key threatened me saying that I should go talk to my manager ASAP before I lose my job. I was completely blindsided. I was intending to talk to my manager in person ahead of time if I were to really leave my workplace. This is the last thing I wanted. I had the most awkward conversation with my manager. She seemed pretty upset. I feel like my relationship with my manager has been ruined now and I have to find a way to repair it. I tried my best to explain to my manager that I would inform her well in advance if I was leaving, and that I really do need a full time job to support myself.

I’m just really sad and disappointed. I feel betrayed by my coworker. If she cares so much about my manager, I wish she just asked me to talk to my manager directly instead of taking this in her hands and deciding for me.

Editing to add that I specifically chose to ask this coworker of mine for a reference because we had a good relationship, or at least I thought so ._.