How do I be friends with my ex boyfriend after a recent break up?

Its only been a week and im having the hardest time of my life..i know im young but dating someone for 2 years dosnt help the situation...i do wanna have time and fix our friendship first but now all we do is fight! I have my senior banquet in november and he was supposed to be my date for the after party..my friend asked him to go on her bus which i was supposed to go on but now im not..so he wants to go on that bus instead of with me!!! I think he is wrong because it my banquet and hes my date but he says because were not going out no more it dosnt matter...does it? I just know that if we go on 2 sepreate buses that night im going to be miserable and its my senior year! HELP ME PLEASE!