From your post, it seems that you hold strong convictions and must follow the path that seems right to you, and that is well within your right. If you must be celibate now, be celibate. In terms of the breakup, just focus on making her feel less rejected. Be kind and understanding; mention your spiritual quest and that celibacy is NOT rejecting her but rejecting sexual relationships in general (if I understood you right). It would be very nice if you told her what you told us, and that is that YOU initiated the sexual relationship between the two of you, and that you own that, but your spiritual path has since led you to want to be celibate; you can mention that there is irony in the fact that YOU initiated the sexual relationship and YOU are the one severing the sexual ties.

So focus on all of that.

To hope that she would stick with you after all that is unrealistic, which does not mean that it cannot happen, but that the probability of that happening is minimal.

So do not hold onto unrealistic hopes and do what you must do for your own sake while thinking of how to make it easier on your girlfriend.

One idea (these things are super sentimental in the world of digital everything, which is why I am recommending them) is to make a hard copy photo book with pictures of your time together and maybe pictures of places you visited together etc. Shutterfly has good deals from now till Christmas and possibly beyond, so if you get your act together, you can, in the next month, arrange your photos on shutterfly, choose a book design, write annotations (maybe they have the cursive font?..), etc. Make it memorable, touching, and thoughtful. A very special parting present is another idea. Whatever she likes that would LAST as a memory - a piece of jewelry, a bottle of her favorite perfume or at least eau de perfume, a knick-knack... only you know what she would like to receive. Think along the lines of your marking the end of an important and positive time period that you spent together and your expressing appreciation of her and adoration of her and wishing her well.