It hurts when love is not reciprocated. In fact if it doesn't hurt then its probably not love.
The paradox is that no matter how much someone may hurt us, we may continue to love them for a long time - perhaps forever.
Nevertheless, it's important that you find some balance in your life - one that allows you to accept her feelings for you, whatever they may be.
Perhaps what you see in her goes much deeper, beyond your relationship with her....
This sounds like a blessing to me, not a curse. Aside from depression, these sort of situations can also be incredibly inspiring - allowing us to grow way beyond our limitations.