> Why does it seem like only gays crossplay?
Just plain old stereotyping and prejudice.
> They reply that they still won't hang with me during the expo and that I still would be gay for some reason.
It's not your friends who can tell you if you are gay or not. That only you can assess.
And if they don't want to hang out with someone that "looks" gay (by their standards) they surely wouldn't hang out with someone who happened to actually BE gay, and that means THEY are the ones with a problem.
Don't let their bigotry dictate your actions.