Let's face it: Just as he has to accept you for who and what you are, you have to accept him for who and what he is. And if he simply can't be romantically involved with a man, then when you start taking hormones, he'll simply stop responding to you in a romantic way. (If he can't be with a man, romantically.) It's not really a choice, I'm afraid. It is his choice to be understanding and supportive of you, and it really shows that he cares a hell of a lot about you to not try to talk you out of it. It's not that strange that he wants to protect himself by trying to reason his way out of it, though.
The problem is: No matter how much you care about someone, and how well you connect: You can't stop instinct. And romance equals sex. (Sex is, to me, not just the physical bit. It's far more complicated than that, and some people don't even need, or want, the physical bit, while they still need the rest. Or the other way around. Complicated.)
Could you have a romantic relationship with someone you feel absolutely no romantic click with?
So yes; give him time. Time to make up his mind. And be understanding if the relationship doesn't hold. On the other hand: If it does, then celebrations are in order!