What's my best move here?

I was friends with this girl for about a year, we were romantically involved for about a month but she had her own issues so we decided to just be friends. It was a good friendship, we always had a good time when we hung out. Occasionally she would have these outbursts where she would get really upset over something I did (e. g., didn't talk to her for a week, was quiet when we hung out) and I always found her reaction of name calling and threatening that our friendship wasn't sustainable with my "negligent" behavior to be a little extreme but I always just owned up to what I did and we moved on. There came a point where I started to think that she was really flirty, but I knew she wasn't ready for a relationship and I don't have casual sex with friends (personal choice) so I never reciprocated. Plus, I was interested in another girl at the time. Things with that girl didn't work out when I realized that I had feelings for my friend, and I told her this and she said "thanks for being honest with me". I took her response to mean that she didn't feel the same, and I accepted it and continued to be her friend. Shortly after, this other girl hit me up again and I decided to go hang out with her. My friend hit me up while I was with her asking what I was doing - at this point I should point out that the two weeks prior to this I hadn't had a lot of free time and had declined my friend's offers to hang out. Anyway, nothing happened between me and the other girl and text conversation with my friend had continued on as normal after that. We made plans to hang out but the day we were going to she texted me that she didn't like being my friend. It was a painful thing to process so I didn't respond for a week, after which I told her that I was hurt by that, but respected her decision and told her I was available to her in case she changed her mind. My question is - what are some possible reasons that my friend decided to end the friendship out of nowhere? And what's my best move here?