A gay man likes me, I am a woman?

He is likely a bisexual, or he completely doesn't know. You're best bet is to wear something very girlish one day to wherever you most often see each other. From that, he'll either think you're trans-gendered, or he genuinely has interest in you as a woman. If the ambiguity still goes on, inform him casually that you're a girl. If you have to go as far as to say something such as "I'm on my period!", at least you'll get your point across, and know fully.