Welcome to Psych Central! I also suggest if you keep having struggles with this issue, then you see a therapist about it, and definitely get some couples counseling before you tie the knot. Please remember she might have had relationships before meeting you, but she is choosing to marry you now. I know you have a hard time believing that, but it's the objective truth. The operative word is "ex." You have a lot to offer, and she must be very happy with your sex life together!