It's a dilemma alright. You haven't mentioned what age group you are in, but from your post I take it you are fairly young.
I guess the best you can do is to let him know that you want to be honest with him, and will understand if he changes his mind, because you don't want to cause him any pain.
I'd give him as much info about GID as a medical condition as you can easily explain, and then it's up to him. If he understands that you have always been a girl who has a few anomalies, through no fault of her own, you should be okay.
Sort of a " I really would like to be your girlfriend, but before we get involved, there is something I have to be ruthlessly, totally honest about....."
Hope it works out. It's good to have a special someone in your life.
Karen.