Dear James Michael,
My experience is the problem isn't whether she loves you or not, or whether she is sincere or not. The issue is how much she loves you. It is also a matter of how much you love her.
If you love her enough, you may be able to accept who she is without leaving. People often leave simply because they don't love each other enough. Wishing you love somebody more than you do doesn't make it happen. The other person has to be able to return the favor.
Of course you never really know until you start offering thoughts and feelings and things to each other, do you, how far and how fast things will work and how you end up tuning in to each others' efforts? I knew somebody once who compared the process to learning to play tennis. I never knew how to play tennis, myself, so that never helped me. After 20 years, I'm still learning from my wife, who's always about three moves ahead of me.
Good Luck, JamesMichael