I think if her needing your religious commitment is important, its important that she beleive its sincere. I think your letter does make it sound as if this is rather sudden.
I think a better way to express belief in God to her right now is
I am working twoards believing in this... I want to be sincere, this is something I struggle with still. I am told it can take time for people to work to the point where they have faith in something they didn't before. I hoenstly don't think I CAN make that happen overnight.. it's been months but something is in me now since I started doing the changes I did. I didn't even WANT to do them at first I was so confused. I did them anyways. Now I actually ENJOY doing them. I really need you to believe that.
You need to belive you are worth the effort, which you are.
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Something aiming at that ... don't make it sound like a light bulb hit you, she's not going to buy that... be honest and tell her you are working at it, and something is in you now that you don't quite understand, but you are happy its there and want to share it with her.
