My ex asked my best friend to prom and she said yes??

Emily
He was my first love, we were together for two years and were supposed to go to prom together, he broke up with me a year ago for someone else and they are still together. 
Getting over him was HARD, especially since I saw him everyday at school. 
He always hated my friend but after the breakup he started teasing her in front of me, and she loves the attention. 
So for some reason they are going to prom together. 
I don't know it seems really odd to me, I don't know what to think about it😳
Now my prom photos are going to have his face all over them 😒