Hi busybee 🙂 you must be traumatize that the idea of seeing him again bothers you. How confident are you to go there? If your confident enough, you can simply avoid him during the party. If not, you can tell your friend and maybe set a schedule wherein the both of you enjoy and have a great time. Im sure she will understand that.

It would be great if you also consider this as a opportunity for closure. You are great, he is fine. You both are doing fine in your life. Everybody is having fun. 🙂 your call 🙂