I was in love with a nice, beautiful girl. We were together for over 3 years. I decided to pop the question, having already bought the engagement ring, figured how to do, you know the works.
Just as I was about to do it, she gives the dreaded 'just friends' speech and dumped me on the spot.
I was pretty heartbroken. I figured what the hell, what had changed.
A week later, while I was still recovering, I saw her together with my best friend. Going out, holding hands, kissing.
So, I decided that was it. I returned the engagement ring to the shop, took a copy of both the receipt I had gotten when I bought the ring and when I returned it and mailed to copies to my now-ex-girlfriend. I had underlined the dates and the words 'engagement ring x1'.
I didn't answer her calls. She stopped trying three weeks later. I figured, if she was willing to throw away three years together in an increasingly serious relationship for a try at my best friend, then she wasn't the girl I wanted to marry. And attempting to fix whatever pieces were left felt futile and too much hard work for too little gain. After all, I would never be able to forget that feeling of betrayal, so indeed friends was the absolute best we could have hoped for.
EDIT: Took me about a month after that until I was feeling okay. Then I realized that I had nothing to be really sorry about. Heartbreak is part of life, I was almost 23, single, had my own (albeit small) rental flat, my good health and my mates. Took me about two hours to organize the loudest party the neighborhood had seen in two years. And considering it was an apartment for university students only, thats saying something. Partying is one thing we do well and with gusto, when we rarely have the chance for it.
For the OP: get over her. It's way past time for that. Stop feeling sorry for yourself, go out and do something you have never done before (for example, bungee jumping, sea cruise), enjoy the experience and once done, shout out 'Life is Good!' from the bottom of your lungs. Then force a smile for the rest of the day if it doesn't come naturally. I swear, by the next morning you'll be feeling a whole lot better.