First and foremost, pay no attention to those who say things along the lines of "You're 16, who cares" and "Just get over it". Those of us for whom the age of 16 is a distant memory can often forget just how intense we felt about our own relationships back then. We (and that includes me) often forget ourselves and look unforgivingly upon the relationship issues of our younger fellows, and we're not right to do so.
The fact is, right now you're sad, chances are you're going to be sad for a long time, too. There's no "just getting over it". All you can do, and indeed all you should do, is just go about business as usual untill it subsides. It won't be easy, and your situation will be there in your head at all times, but you shouldn't let it change your day to day life or you'll just end up wallowing in it forever.
Here are a few tips you can follow;
Put on a brave face. Even if you don't believe it yourself, keeping your spirits artificially high will encourage those around you to treat you as they usually do, which will hasten your return to normality.
If your friends try to cheer you up, let them. Nobody likes a mopy loser who can't talk about anything but their ex. Let them tell you their dumbass jokes, laugh at them, then play Halo or go to the movies or whatever it is you normally do.
If you have to talk about it, and you might - we're not all the ironhearted soldiers we like to think we are - then talk about it a little to someone you trust. Get it out and get it over with, then continue as normal. If you have a friend that won't betray you, then talk to them. In this case, however, you may find your parents are your best choice.
Don't try to "ease yourself out of it" by keeping in contact with her any more than necessary. "Just being friends" never works out. If it's over, it has to be over. Similarly, don't try to replace your relationship based activities with something else. For example; if there's a time of day when you'd usually call her or go to her place, don't purposely replace it with a videogame or whatever. You'll only begin to associate that thing with your absent relationship.
When the typical thoughts of whether you'll find anyone else inevitably arise, do your best to ignore them. The truth is, you almost certainly will. Even the worst of us end up in serious relationships - or, worse still, married - at multiple points in our lives.
Last but not least, the thing that should be most comforting to you is something that you'll need no advice to understand. Whatever the cause of your upset, be it a breakup or a broken leg, it will stop hurting eventually. Nomatter how much it hurts now, or how long it's going to last, eventually, it simply won't hurt any more.
So! For the time being, stand up straight, stick your chin out, and get on with it as best you can. No one's looking down on you, son - it's happened to all of us.
