I've been in this spot before mate. I hate to say it, but I think the window of oppertunity has passed. You do something drastic, you could loose both her respect and your best friend. Chances are she has thought about you at some point in time, and no offense, hasn't had the same feelings you do about her. Wait this one out. If it's like the case I had, they will break up and you, as the best friend, will hear all sorts of things about her you never knew to be true. At this point, you will realize she really isn't worth all the hassle. If they don't break up, you will still get all the props in the world from you're buddy for being so cool about this, thus he owes you one.
Buy a tradmill and a weight set and take all those feelings out on yourself. I mean really kick your own ass. It's gonna suck, but the pay-off is worth it. You'll feel more confident and it'll take your mind off the problem. Before you know it, you'll be looking good and meeting women all the time. Then maybe one day they will break up, and you'll be there to comfort her when she notices "damn! This guy's made some drastic changes for the better of himself." I'm not calling you meak by any means, I don't even know you, but now is the time for self-improvement!
Nietze once said the most depressed mind is the most realistic, and thus, the most proactive. For the next month or so, it's the SmoothNRK show!!!!
If you can't tell, I just ended a long-term relationship recently. It always hurts no matter the circumstance, but tomorrow is another day.