This doesn't sound like a disorder. It sounds like you just have difficulty getting aroused with women. You may find it intimidating or you may simply not find these women very arousing. Rather than setting up an elaborate scenario where you engage in sex with first a man than a woman, I'd suggest you focus on one or the other. If you feel compelled to have multiple partners in a night be very cautious about protection.
Also be sure you're comfortable with the person you're going to marry before you agree to a lifelong commitment to them.