The only thing I can say is good luck to all. Nothing less will do. You can and should share with her why you don't and never will believe in the Mormon church, and let her decide for herself, but be prepared to have that blow up in your face.
My mother now uses her time in saving stray dogs and helping the poor while my father is away which is everyday. I have finally learned to pray to change my heart, not his. No sex before marriage. This sub is a great place to do that. Honestly, the bulk of what I did was pretty routine and uninteresting. He could come home from trips and I was too worn out to fake the good cheer.
Marrying a non-Mormon is not something you do it is something that happens. I am dating a wonderful man, amazing. And depending on his views of the Sabbath, you will probably get the tug of war on Sundays. The history of racism and violence is upsetting. The submariner's wives are in a similar situation.