Turning 18 please give me some advice to get rid of this bitter feeling

So I had been dating this girl for a year, and half way through she started acting kinda odd. She had a guy best friend that moved but she told me they still talked a lot. One day we had a class reunion where the best friend was also there; I actually never got to see her during this reunion and I kept texting to ask if she wanted to hang out afterward. Her replies were super vague and occasionally she’d say “I’m talking to my friends”. Nothing happened until the reunion ended and she asked me if I wanted to hang out with her and her best friend(without the slightest hint of her wanting me to actually go). I replied “no, just go hang out with your friend” then a couple days later she said “I was sad when you let me go like that”. I didn’t understand what the actual fk she was talking about when she said that. Shit escalated and I wanted to talk things out but all I ever got was “idk how what to do as your gf” to which I didn’t understand either. Eventually I guess she got sick and tired of trying to work things out and screamed “you miss the time when I was enthusiastic(or something similar in meaning) about you, don’t you” I broke up with her, but a few months later her friends all said she broke up with me because I was being an ass and boring.

Sorry for the pointless story. I wanted to get this out there. If you read it, what did I do wrong? Thanks!