AIO for telling my girlfriend’s mom she cuts herself in front of me, and then cutting her off?

​I need a reality check. I’ve been feeling like a traitor, but I’m starting to think I was just a hostage. ​My ex-girlfriend used her own safety to control me. I have stood there, paralyzed, watching her literally cut her own wrists with a blade right in front of me. Whenever I tried to leave or we had a conflict, the blade would come out. ​It reached a point where it affected our intimacy. She would ask for sex, and if I hesitated, she’d make a cutting motion across her wrist until I nodded and complied. ​The lowest point: She threatened to block me and told me to "beg" for her to stay. I was so mentally broken that I actually got on my knees, groveled, and bowed my head to the floor. She blocked me anyway after I did it. ​I finally reached my limit. While she wasn't looking, I told her mother everything. I told her that her daughter was cutting herself and that I couldn't be the only one responsible for her life anymore. I felt like I had to "snitch" just so she would be safe and I could finally breathe. ​Now I’m trying to rebuild my life. I have chronic dark circles under my eyes from years of stress—starting from my childhood when I’d stay up all night to mediate screaming matches between my mother and sister, and then years of this relationship. My body is exhausted, my feet are sore from trying to start an exercise routine, and I feel guilty for "betraying" her trust by telling her mom. ​Am I overreacting by feeling like I was abused? Was I wrong to tell her mother about the self-harm just so I could leave?