Hey,
So this will be the first time I'm responding to this thread but definitely not the first time I've read through it. It is crazy interesting. I have a few possibilities but I'm almost 100% sure that the last one is right.
Theory 1 (not likely) He is straight but is ridiculously comfortable with it and has found a "bromance" (god I hate that word but it works so well) with you. He likes this girl and wants his best buddy to share that with him. Given this scenario, you gotta move on or begin to find flaws with him so you can move on. But you won't be able to do that, will you? Ultimately, you'll end up telling him and ruining what he thought was the perfect friendship. He'll get over it but you probably won't. You'll feel like shit in the short run but OK in the long run. You lose the battle and win the war.
Theory 2 (more likely but still doubtful) He wants you and wants things to progress but is scared, like you I might add, to come out and do something about it. He made out with the girl because he's either bi and hasn't gotten any waiting for your ass and/or wants to make you jealous, which would be working, and solving this problem would mean you would tell him you want him. Or, instead of directly telling him, you could JUST tell him you are gay and see if anything changes between you. If it is case numero uno, I still see him getting past this because of your deep friendship. You win or at least lose the battle less severely because you have a stronger bond and then win the war.
Theory 3 (what I would bet on) You are in love with the idea of him and love telling people about it (two ideas that have been stated on here) but you take it a step further. Trust me, I've been there, for 3 years to be exact. The problem with my situation was the girl (I'm bi) I was in love with lived 1,017 miles from me and I always thought that if I could get the opportunity for a real relationship with her my life would be complete because I loved her. I still love her, but as a friend. But enough about me. You have him right there next to you and you can hang out with him but you won't do anything. Why? Because you actually like being where you are. You like that everything that has gone wrong because it's not YOUR fault. If you don't do anything, it can't be your fault. This is the first area where you are wrong, doing nothing IS your fault! Then you come on this website and tell everyone about this great guy you could get with, but you just can't because everything around you just sucks that much and the world is out to get you. Dude, the world is not out to get you and your man. Your just trying to get other people to believe that so you get attention. But with attention comes people like me who actually want to give you advice that works. They're telling you what to do and you LOVE that attention people are giving you. But because actually using one of their ideas, should they end up not working, losing would be your fault for actually listening to them and you couldn't live your love story anymore, the one where society has it out to get 2 people but they overcome all the adversities. I'm not trying to ruin your fantasy, fantasies are the only real reason for living, but I am telling you to either prove me wrong and fucking kiss the boy already, either losing the battle and winning the war or BOTH, or to move onto another fantasy.
Theory 4 (which I thought of when I was writing this lengthy reply) I'm a freshman in college aka I was just in high school. It is REALLY REALLY early for a prom of any kind. No one will get mad if you admit this isn't true and there is a problem because the only reasons why people reply to this thread is because they love drama, in which case they won't really care if this is all a lie, or because they genuinely care about well being. Go see a psychiatrist and you'll win the battle and war.
To summarize, you win the war given any of the situations I've described here.
THE ONLY WAY YOU DON'T WIN IS NOT DOING ANYTHING, proving Theory 3 correct but I'd much rather get proved wrong and see someone happy. I REALLY REALLY REALLY hope I'm wrong with the last two but they seem to fit. Regardless of the scenario, just fucking do SOMETHING and feel better kid.