What should I do if someone wants to hookup with my prom date on prom night?

Ok, so I'm a senior in high school and have asked a very attractive girl to prom who I have feelings for. However, one of my friends has had ever changing opinions about this girl and at the moment I asked the girl out suddenly reverted to wanting to hook up with her again. As soon as I asked the girl out I had suspicions and worries that the guy I'm talking about would try and pull something very sleazy on prom night and try and hook up with her. However, I believed that because we were somewhat friends he wouldn't try such an underhanded thing. I started talking to my friends about my suspicions and they all agreed with me that hooking up with my prom date would be a really sbag thing to do. My suspicions ended up being confirmed recently when my best friend told me that the guy had asked him if he thought it would be a bad thing to hook up with my prom date and later again told another of my friends that he was going to try to on the night of prom. This guy I'm talking about treated me like crap for about 6 years of my life and we have only recently resolved differences and become somewhat friends. I still wouldn't trust him as far as I could throw him though. The girl does have some feelings for the guy but also said that I was one of her top choices for prom and did after all accept my proposal. I don't want this guy to ruin my prom and honestly I was hoping to maybe hook up with this girl. I like her and actually have some feelings for her outside of looks. I don't want to get into a relationship right now because I'm going to be heading to college soon. I understand that it is none of my business as to if she hooks up with the guy on any other given night, but on the night of prom when she's my date I really don't want to be made a pushover and have my date poached from me like that. All I want to do is enjoy prom, maybe hook up with this girl, and definitely not have someone else hookup with my prom date on the night of prom. Should I confront the guy about it before hand? Should I sit back and see how things unfold? Should I stand up and stop the guy if he tries anything on prom night? I'm asking you guys a simple question; what should I do?