What do guys expect from their prom date?

I'd say it doesn't matter what he expects. It only matters what you're willing to give him. And honestly, prom isn't a good enough excuse to sleep with a guy. There are far too many emotional, spiritual, and physical checks that get cashed when you do that. Make sure that your prom experience is fun and full of good memories, not regret and emotional scars.

As far as dancing with other guys goes, have a great time and enjoy yourself, but make sure you don't piss him off. It depends on how good of friends you guys are, and whether there's any potential for a relationship. If you are just friends and don't want to date, then by all means dance with other folks if their dates don't mind.

Old-school societal rules say that "a lady never leaves her escort" (Frank Sinatra, etc. ) - but that's definitely no longer respected or honored. If he is taking you as a date and took the initiative to ask you, you should at least do him the honor of dancing most of the time with him.

You talk about it up front. If you and the guy make it clear that you are going as "just friends", then no, he cannot expect sex from you and you can dance with other guys at the prom. If you are in a relationship with the guy you go with, he will probably expect sex and it wouldn't be a good idea to dance with other guys.

Basically, it all depends on how you guys decide to go, as friends or as a couple.