Ex and I are always doing this, help please?

ok so my ex and i broke up about half a year ago. it was bad. she told me that she needed a therapist and antidepressants because of it and yeah she showed me the prescription and everything, she wasnt lying. about 3 months after the first break up we started talking again. things were great for about 3 weeks to a month and then everything crumbled again. another month and a half goes by of no contact (till last week) and i started talking to her again cause it was her birthday. we started talking up until yesterday where she suddenly calls me and tells me that "I always do this, everytime im getting better you come along and screw everything up" very emotionally. its always so sudden where everything is fine one second then hell the next. Im now blocked from her life again. i lost her already and i dont want to lose our friendship too. thanks for your time and advice