I really like a girl so much it physically hurts me inside. She is the most perfect person I have ever met. We have several common interests (music for example), the same sense of humor and similar interests. We are not going out but are friends, we get on well and talk often. When I am not with her, I feel empty - if that makes sense - like there is a large part of me missing, and when I feel like this I seem very depressed, I have also been informed by friends that I seem very distant, I am also not motivated to do any work, eat or sleep. I should also say that I am unbelievably shy and find the whole “tell her you like her” approach incredibly daunting. I’m sure that if I play my cards right and I let time take its course then I could work up the courage to ask her out, but my problem is one of my best friends also has these feeling for her and has known her much longer than I have (May I also add that they dated briefly). Now, I would give anything to be with this girl but I also don’t want to lose any friends, this being said, I would through my friend under the bus - metaphorically of course - to be with her. I really don’t know what to do and I don’t think I can take this ‘empty’ feeling much longer. Its killing me inside. Everywhere I go, everything I do, I think of her. I can’t listen to any form of music anymore without getting emotional. What do I do?

Dude, just tell her, or you will always regret not telling her once your friend has made his move. You will feel much better knowing whether she shares the same feelings. If she doesn't, you won't have to worry, because you will just be set into the friend zone. Trust me, do not wait. Just write out what you want to tell her and recite it so you don't screw it up when the time comes. If you don't tell her now, you will have to go through the pain of dealing with her asking you for relationship advice once she has found someone else. Be brave. She will respect your bravery. Hope this helps.

Why are you so concerned about your friend? Not only does it not matter that he has 'known her longer,' but he has already dated her, and she apparently put a stop to that or they'd still be dating. So I don't get your hesitation on that score.
Now as for shyness - I also don't understand why so many young guys feel that there has to be this quantum leap into 'asking her out on a date.' There are countless little ways to sneak into that realm that is just over the line of hanging out as friends. Any little event that happens alone with her is in effect a date, whether it's going for a walk or going down the street to buy a soda. You walk, you talk, you sit on a bench, you have a good time without others butting in - that's a date. You say things like 'that was fun' and 'good grief, we were gone 2 hours, it felt like 2 minutes' and all sorts of clues to her that she is special. She will give little clues back. That's how it works. Little clues that progress toward a romance.