Have you told your fiance what's going on? Maybe it wouldn't bother him as much if he knew that it's not him you're withdrawing from. And maybe he can help you with this, by letting you be completely in charge, directing him to do what feels good at the moment.

Beyond that, it sounds like your trust has been violated, so your mind and body are working to protect you - not necessarily from your fiance, but from a situation in which you feel vulnerable. Can you think of experiences you've had, either in childhood or as an adult, that make you cringe when you remember them? They don't have to be sexual experiences to affect you sexually. Even if it's something small and you feel silly for letting it bother you, a violation of trust can still cause problems. This might be something to discuss with a therapist.

Also, you might want to have a physical examination, to rule out any possible disorder that could be affecting you.

Best wishes!