Re: In love with a girl who has a boyfriend
I agree with what others have told you, including the comment along the lines that "this too shall pass," and while it seems huge now, it won't later. Everyone has to go through these stages, no matter how many people tell you that you'll look back on the situation and realize it's a teenage thing, you have to live it for yourself and don't have the benefit of experience and hindsight to understand it. You're working out that learning process of handling all kinds of complicated relationships, and you can learn from this one. I think the most important thing is that everyone treat each other with respect and dignity, even if others don't treat us that way. You can't do anything about her behavior, only yours, and in the end, it's your own spiritual journey that matters. Start racking up your good karma now!
I'd also like to add one more thing - being away at camp - even for adults, really intensifies any situation. Your world shrinks to this little universe of whatever happens inside that context, and weeks can seem like months or years, heavy relationships and friendships develop very quickly, and they often don't translate once you are back in the "real world," when your routines go back to normal. I've filed those experiences away as nice memories.
I went to something like a camp for artists when I was in my 20's, and I hung out with a guy there for awhile - mainly because he was good company and had a truck, while I had no transportation for my 2 week stay. Having done nothing remotely romantic with him, much to my surprise, he told me he was crazy about me and gave me this long love letter when I left. I was floored because he was married and about to be a father - his wife was due to have his baby any day, so clearly he had other commitments. The previous week he was going after some other girl. He had an agenda for that 2 weeks of "camp" that had nothing to do with me, really. In retrospect, I think he was flipping out about becoming a father at such a young age, possibly got married too young, and this was his inappropriate way of trying to deal with it.
I don't know about this girl you like, but it sounds like she has other commitments in a similar way, and now that everybody is home and you're not in that un-real world of camp life, things are different than you thought. It's just how it is.... you'll come to realize that and be able to let it go. If being friends doesn't work for you, it's OK to move on and you should.