focus on the girl you are destined to meet next, and how you are going to be at your best when you do meet her. let go. it's a long journey and you are statistically obligated to have your heart broken along the way.
if all else fails, a few drinks and a few family guy episodes can work wonders.
Remember if you are committed to each other, there should not be another one in between.
Think about how much happier you could have made her..too bad she'll never know. And after think about a girl who you like and that deserves to be happy... and make her yours :) Don't waste your love/thoughts on someone who doesn't deserve it.
Well if you don't then go out more often, meet new people, discover new things...My point is try to find someone who deserves your love, not someone who's in love with someone else, while all you do is think about her and her new lover. Try to tell yourself that she'll never get to see the best of you..someone else will. someone that deserves your love as well as you deserve there's..