Uneasy and a bit jealous of my good guy friend and my former best friend?

Try finding a date for the event someone that does not want to be your boyfriend though. Then that would just make the situation more comlex to solve. Just be cool and don't let him know in the least that it hurts you. If you don't mind you have a crummy best friend to do something like that just to hurt you. There is a reason why he is not yours. I believe there is someone much better for you than him. I hope you feel better soon.