help!!!!??

so my best friend and her bf broke up and her bf and i had a good terms friendship during when they were together. my best friend broke up with him but they both agreed to get back together if they wanted to two weeks im the future. not even two weeks pass by and like two days after the breakup, her ex bf tells me about a girl he is gonna ask to homecoming dance!! i suspected it mightve been my hest friend but then a few days later after that, at the two week mark they agreed on, my best friend comes crying to me telling me that he didnt wanna get back together. i understand that nothing could have been helped at this point. what im angry, super angry, about is that he had asked some freshman out to homecoming and had the AUDACITY to tell my best friend what he was planning to do for that freshman girl and how his friends already ship her with him. im so angry and i dont know what to do because my best friend is sad, my friend? (her ex bf) has now shown me that hes not even worthy of my best friend, and im just stuck here worrying. they were together for a year and to just move onto someone else in a matter of less than two weeks... im super salty!! im not mad because he didnt wanna get back into the relationship. im not mad at the freshman girl. im f*cking mad about how he has been so inconsiderate of my best friend's feelings especially when she wanted to get back together with him. he literally asked that girl to homecoming in front of everyone at school and didnt even care to consider my best friend's feelings.