Hi everyone! OP's GF here :))
I wanted to say thank you to everybody for the encouragement (and to the people accusing me of abuse as well, because those replies were actually pretty funny; I would never do anything to hurt OP, nor would I ever force them into helping me deal with my episodes. I'm working on learning to cope with them healthily and have been able to, at least recently, go a notable amount of time without self-harm).
I talked with OP about it when it came up and had already decided on not going back, so this post was more about feeling more confident in my decision; a number of my coworkers, some of whom I consider friends, have tried discouraging me from quitting, which made me doubt my decision. I've been at this job for a long time and have grown close to the people I've worked with (yes, including M), so this hasn't been an “easy out” situation.
And on the note of going to therapy, that's next on my list! I have a psychiatrist and am working on finding a therapist who suits my needs. I struggle with a lot of issues related to anxiety, people-pleasing, and self-worth (none of which are new to me, as I've had these issues since childhood), so I'm hoping to be able to discuss and improve them with the help of a professional.
Again, I thank all of you for your encouragement, and to OP, I love you so, so much <33