The girl I am going to prom with is still stuck on her ex. This is problematic because I would like to be more than just a prom date.
Her ex crushed her. They dated for over 2 years work, then he broke it off just two days after saying he loved her. And the day he dumped her he started flirting with one of her co-workers and is now dating that co-worker.

My prom date is beyond confused. Her ex lead her on said he loved her said he wanted to spend the rest of his life with her, then suddenly nothing. She is really stuck on him even though countless people have said that usually you deserve better, he's not good enough for you etc. Please help. Idk what to do.

Dude, you, and him, and her are all in high school. You will not (statistically speaking) spend the rest of your life with anyone from school. As for her, you go to prom as you have promised, then back off after prom until he's out of her system. Right now, you are just the guy she's stringing along until she realizes he's not coming back. She can't respect that, so after prom leave for awhile then in a few months see what the status is.

You cannot help her so just be a good prom date and have fun, and don't expect much from a heart broken girl. Time heals, you cannot. She needs a friend, not a guy to replace an ex.