Kind of a tricky situation - what should I do?

Definitely be honest with him about how you feel. Explain to him, that this is a really special night and you don't want to have any negative vibes about anything. Get a feel for what he thinks about just taking the bus... if he seems like hes going to guilt you and be pissed off, he shouldn't be your date. If he is understanding and says he doesn't care then thank him and offer to explain to the girl why you can't go in the limo so he doesn't have to. And when you're explaining to the girl why you cant go, don't tell her the truth because she's a frenemy and won't be understanding of you, just tell her you already paid for the bus and are meeting friends on the bus and that you should all hang out at prom. Just be confident in whatever you want to do, and do it! Enjoy prom and if you end up choosing to forget all of this and go into the limo, just be patient and remember that even if there is a jerk in your limo, remain thankful. Appreciate every moment that comes with prom, your dress, dancing, drinking, whatever. If the guy does something annoying then just laugh at him and think to yourself "thank god i'm almost done with these jerks at this school and off to college". xoxo.