If it has been bothering you for months then it is not a stage, it needs to be addressed. Do you see a therapist to help you think things through?

You don't want to hurt your fiance but he is definitely going to be hurt if you marry him when you have someone else on your heart and you are questioning whether you even want to be with men to begin with.

From what you say, it sounds to me like your heart is telling you to apply rhe brakes and spend some time figuring out what, and who, you truly want.