[Eternal]

So I'm bisexual and my boyfriend has known this. Well recently I told him I think I prefer girls, and he got pretty upset by it. He said it wasn't a nice thing to say. I don't really understand why it was such a big deal though, I still like men too? It's just like if I said I prefer black hair when his is brown. To that he said "yeah but it seems like you're wanting them to change instead of accepting who they are in that scenario." Now I'm upset because I feel invalidated and like I'm not allowed to have my gender preference. I obviously like him, and I've never asked him to change.
He asked his best friend (who is also a male) what he thought, and he agreed if he was dating a girl who is bi and she said she prefers women, he would feel uncomfortable. On one hand, I can see where he is coming from (although I don't think I would be upset if I was dating someone who is bi and prefered the opposite gender), but on the other it doesn't mean I only like women, and like I said I feel almost like I'm not allowed to like what I like.

I'm wondering what other people's opinions are on this.