If you lose him because of your sexual interests, what have you really lost?

Besides, you could lose him over religion, politics, the next person to come along that has more chemistry (with you or with him,) or bad housekeeping, cooking, or idiosyncracies (by or of either.) Sex is so important to a good relationship that if you have needs he doesn't, won't, or can't meet, do you really think you want a long term relationship? What if his kink or fantasy squicks you out? Would you really want to stay with him?

Therefore, it is better to find out now, before your're so hopelessly in love that you sacrifice your long term happiness for your long term happiness.