My ex-girlfriend is going to screw me over

So I've recently been dating a girl, we started dating on the 17th (of November) and she quickly made things move quickly as I've realized I don't like. I thought I had a crush on her, and through the experience of dating her, I've realized I actually do not like her at all. I've realized I'm not just asexual, but aromantic also. She moved things way too quickly and she told me that she loved me the day after she asked me out, and I thought it was scary but I ended up saying I love you back to her because I didn't know what else to say to her. Things went way too fast and she kissed me the second after she asked me out, and I lost my virginity that weekend. Way too fast for me. On Tuesday I wasn't there for some of the school day and she assumed I was avoiding her, my best friend told her that she could go a day without talking to me, to which she started crying, screamed "No I can't!" and walked out of the room, proceeding to punch a wall and get very angry at me. I saw her after school, she said she was very mad at me earlier (even though that morning I tried to talk to her but she left so it was actually her fault we didn't see each other, but whatever) and then walked away after telling me to give her a "real kiss", but whatever. So she didn't show up Wednesday, to which I was mad because I was going to break up with her in person. I didn't want to over text but seeing as she broke up with her ex-bf before me over text, I thought she would'nt care either way. I would've liked to break up with her in person, but I was scared she would hit me as she has been known to over react and manipulate people before (punching the wall and a friend actually warned me about going out with her, I should have taken the warning) and since I was too stressed earlier, I broke up with her over text because once again I thought it would be okay and I couldn't deal with that thought clouding over my mind until Monday. I explained that I was stressed, she said it was okay and she was happy I had the guts to tell her and I said we could still be friends, whatever. Later my best friend texted me asking if I was talking to my now ex-gf, to which I said I wasnt, and my best friend sent me a screenshot of her saying "I'm single now" with a whole bunch of crying emojis, and then ending with a question of "what's the easiest way to kill yourself"
I don't believe she is serious, since my friend that had warned me about her told me she was manipulative, and she's quite obviously mentally unstable (also she told me as much but she has more than just ADHD) What am I supposed to do in this situation? If she actually kills herself (if she was asking how, i doubt she'd be successful either way) then she's going to mark me down as the worst boyfriend and say I fucked her over and everyone would hate me and I would be outed and in result would end up with the same fate as the whole Leelah Alcorn incident. She most likely won't, but either way, what am I supposed to do in a situation like this?