Anyway, you got yourself a treasure. An interfaith marriage can be done well or disastrously, or even only being made up as you go. Now learn about how all of your doubts can be resolved through apologetics. Besides the obvious brain damage that you will be made to suffer your entire married life, there are future kids to think about. What am I getting myself into.
You've stated that she had numerous guys break up with her after she took sex off the table. In fact, your GF is probably one of the countless Mormon women who get married only to find out they have zero sex drive because of what they learned growing up. Certainly there are such people in the church, but there are such people in any organization, and I would challenge you to remember that the members are also individuals with thoughts, feelings and the ability to rebel in their own ways.
I appreciate knowing all you have mentioned since it gives me a bit of insight and some real good tips. Also, I know a bunch of Mormons that say they are, but don't act like it. A lot of Mormons escape that pitfall and can put people first. Make an honest effort, and see if you reach the walk-away point. You have to make the decision as to what you want your home and your children to have in that home.
The "loneliness" is not an issue for me. Every bishop, new set of missionaries, home teacher, etc. Initially I thought he would join the church and life would get back on the only track I knew. Ask questions, try to find out as much as you can.