Wait till one of the following moments:
-after he's blown a wad of money on dinner for you, or
-in the middle of being romantic
and say "by the way honey, I'm a DG. Do you still like me?"
If he walks away from you because of it, then he is the superficial one, and not worth your time. He met you and it didn't even cross his mind that you were Greek because you didn't live up to his narrow stereotype. He assumed you weren't in a sorority. And you know what happens when we assume.
