If an official status had to be slapped on it, would it not just be.. something along the line of best friends? As primary school as that sounds. I know I'd get a teeny tiny bit jealous if any of my bloke mates (I'm a girl) were to get a girlfriend, initially because of the prospect of being unable to spend as much time talking to them or whatever, and then because of a feeling of rejection on some level, simply because I'd never advanced past the friend stage. Irrespective of whether I actually wanted to or not, the feeling of rejection would still be there.
I know that a lot of people's ideas on what a relationship is vary, but I can't see the boyfriend girlfriend approach being realistic if you're still going to effectively be close friends on a platonic basis. But then I guess it's ultimately up to you two to establish the terms, and if both of you agreed to be boyfriend and girlfriend, I'm not sure what technicalities could prevent you from carrying on being just that.
Many people are of the opinion that it is actually impossible to maintain a platonic relationship with somebody of the opposite sex without either both, or - rather more messily - one of you, developing that extra something for the other person.
Standing inside that mindset - perhaps he's in the closet?
If not, I wouldn't worry about defining it: you're close, and would hate to have some dint by another person threaten the bond you have with one another. Ignore the people who don't want to accept it, they're either narrow minded or desperate for gossip. They should just suck it up.