I'm sorry bud, but I've got to agree with the rest of the board on this one. As much as it hurts to break things off with this girl, I'm afraid it will only get worse for you in the long run. You sound a lot like me in my situation with my first wife. "Sexual hang-ups...but I love her so much...things will get better...etc..." I went through all the arguments to stay together and why our marriage was "good." Truth is, it sucked ! It was only a matter of time before resentment not only from me, but from her as well began to creep into our relationship.
Not saying this will happen to you, but that resentment built up over the years until finally something had to give - she did... and into the arms of another man..and still with the same sexual hang-ups so that lasted a very short time.
Unfortunately for me, I was already into my marriage and thus a little more committed. YOU ARE NOT THAT FAR IN YET !!!! Run...Run like the fcking wind !!! {sorry, I just saw 7 or 8 years of my life that I wasted go rushing past me, and given my current situation, I would REALLY like them back about now } Of course you love this girl, have strong feelings for her, don't want to hurt her but you also have to think about YOU and what kind of marriage you're going to have and what might happen down the road. I'm not afraid to say it, my wife knows it...but yea, I still have some feelings for my ex-wife... we shared some special times together but do you really want to take a chance on maybe things miraculously changing? And what happens when they don't change, only now there's children involved?
Take the special times you shared, cherish them, they're a part of who you are but seriously think about ending this. And if you do, try to do it in a good way without a lot of anger...you'll both feel a lot better about it in the end. Think about it pal. Good luck to you.
BTW, I might have missed it but how old are you two?
} Of course you love this girl, have strong feelings for her, don't want to hurt her but you also have to think about YOU and what kind of marriage you're going to have and what might happen down the road. I'm not afraid to say it, my wife knows it...but yea, I still have some feelings for my ex-wife... we shared some special times together but do you really want to take a chance on maybe things miraculously changing? And what happens when they don't change, only now there's children involved? 
