Discussion: Fallin for my roommate...need some advice!

I have lived with my roommate for 14 months, and known her for about 18 months. She is my best friend, we get along great, and do everything together. So much so, that some people dont believe we are not romantic. We both got out of bad relationships not too long before we met. She has been occasionally seeing her ex for the past year. She has said she still holds feeling for him, but he does not feel the same. I believe she is somewhat shutdown emotionally because of this. But guess who's there to pick her up when she is down?...thats right, yours truly.
Anyways, here it goes... It seems like every day my love for her grows, and i couldnt picture life without her. I dont think i could live with myself without knowing if this beautiful lady, who makes my darkest days light, and I could be happy together romantically. But i know she doesnt want to risk our friendship, because we depend on each other so much. I want to bring this proposition to her, but i dont know how. And how can i ensure her, or even myself, that we will still be ok if it doesnt work out??
Any advice, or experiences would be so helpful!