I agree with Spacial.
Most guys don't want their female partner to fight their battles - that's part of being a man to many (not all though - there's plenty of variation).
What you can do, and will help, is to continue to recognize him as who he is. I don't know how well he passes, but if people get his gender wrong, you can head some of that off two ways. First, you can take advantage of the heterosexual imperative - basically if you're doing stuff like holding his hand or being affectionate, and people see it, and they are not sure if he's male or female, seeing him with a female makes them more likely to think he's male - particularly when both are playing the roles of heterosexual mates. The other thing you can do, you can make sure to inject early in conversations the appropriate pronouns and terms. For instance, at a resturant when the waitress asks where you want to sit, you can speak up and say, "I'd like a booth for me and my boyfriend." You can do both of these around family and such too.
Basically, by you showing that you have no doubts, people around you will see your confidence and that will help them "decide" one way or the other. Now of course if he passes really well, some of that isn't needed around strangers. But showing the confidence and making sure to use male pronouns and such will let people who do know his past that you've already "made up your mind".
