Please Help Me I'm Devastated

My best friend of four years and I are no longer friends anymore. We are both 17 and in our final year of highschool. We were generally quite negative and pessimistic people but we "bonded" I guess through dark humour and such. We were absolutely inseparable throughout almost all of highschool, our personalities complimented eachother and we just always got along and had so much fun together (for the most part). However, lately I've been in a pretty bad mental state and she basically sent me a super long facebook message earlier today about how she doesn't want to be friends anymore bc I've been affecting her mental state. Of course I'm extremely heartbroken to have to part ways with my absolute best friend, but if it was best for her, I'd of course want her to be happy. So I agreed and said my goodbyes and that I hope she's able to grow into the wonderful person I know she can be. THEN, she says something along the lines of "wow, I thought you'd fight for our friendship, glad to know how much you really cared..." and starts getting angry at how I "didn't care about our friendship" (I don't fully remember, I deleted the messages). Like what the hell ??? I agreed to part ways because I wanted her to be happy, and then two seconds later she hits me with a "blah blah blah you never cared" what the shit ? That doesn't make any sense.

I am heartbroken. She was my soulmate. She wants to completely break off the friendship AND blame it on me for "not fighting for it"? That's messed up. I'm an extreme mix of angry and sad right now. I don't know what to do. I'm devastated.