My best friend is dating my exboyfriend?

so thi story is really really long, but ill shorten it. so me and this kid went through a **** load together and sadly it ended in thee worst, we broke up and he wont look/talk to me and i refuse to tak to him& all that. anyway i cried over him sooo much and my friend at the time jenny was there for me some of the time. now she is my BEST friend and she is dating him. i told her i couldnt control her life and her to do what she wants so theyve been dating for 5 months or something me and him dated for a year and a half. but our realtionship lasted much longer. weve been on and off and all that forEVER. but in the beginning, i told her i didnt wanna talk about him or look at him or see them together, but i cant get away from it due to the fact that its high school. so recently ive learned to put a false smile on my face, but i want to pain to go away. i cant go a day without seeing them and wanting to scream or cry and i hate being like this all the time when shes happy 24.7 he's such a liar but she falls for it. he's her first boyfriend.