Oh Intra, that's horrible *HUG*, I'm sorry to hear that
I understand why you don't want to go because it would take a lot of confidence and or anger to manage it but if the prom is important to you, perhaps try calling some friends and letting them help you abit to feel better and not let him ruin it for you, although of course thinking about it and seeing it are two different things. It really depends on whether you feel strong enough and if you do go and manage it, it might help in the long run to get over him, but don't rush yourself. If you don't feel ready, you know that there will be other events for you to go. It might also help to take some time to think about what really caused the breakup, if anything, so you can let him know exactly what you think and then try to move on.
Just bear in mind, that even though it feels terrible and intense, you are (honestly) young and it's better for you not to get too emotionally involved just yet. Easier said than done maybe and I know that you already have to an extent, but you have so many possible doors and new people ahead of you. Cry/talk it out or mull things over but try to think of tomorrow and days to come when you will feel better.
Maybe do something that always makes you feel better, channelling this kind of emotion into an activity or something positive tends to have a healing effect.
