Well sorry, but you're being completely selfish to not tell the man you're going to marry that you can't have his children. Have you discussed each other's wishes about having or not having children? If so what were his expectations from the woman he is choosing to spend the rest of his life with?
Seriously... you tell him and you let the chips fall where they may. If you love him, you will not hold this information from him for a moment longer.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion