As DeeAnn stated, it just IS… sexual orientation and gender identity are two different things. I am attracted to woman, but I have also found myself fantasizing about men… Whether this is true attraction (i.e. I am pansexual) or just a way to justify myself as a woman, not sure. It could go either way until the rubber hits the road (i.e. I have sexual relations with a man).
Good luck! and remember… a loving relationship is never built on gender… it is built on trust. be honest with your partner and be the best person that you can be and enjoy your time together!