I went through the same thing last year. It still sucks, and it's super-hard. It lasted for months and months before I was honestly ok. Told her how I felt about her, she told me how awesome I was but it wasn't happening, then had a huge public discussion on her Facebook with her friends about how she couldn't find anyone worth shit and she'd probably be forever alone because nobody liked her.

I threw myself into music because that's how I express myself, wrote every sad piece that I could, there's no happy ending to it, though, just doesn't sting as bad now. I'm sorry you're going through this, but know that you're not alone and it happens to us all.

You have value and it's not based on whether you're with that person or not, even though it feels that way right now. It's all about the perspective. Look at it any way you can to make it not hurt as much, like you were never with them earlier in life and you were fine, and you're going to be ok in the future, too. Whatever it takes to change the perspective.