Sorry that I'm a guy replying, but I'm an AS guy with an AS girl. And surprisingly enough, we both contribute equally to romantic stuff (Well, not exactly equally, but what is ever exactly equal? I might be doing 52% of it or 48% of it, but that's close enough). Yet I don't think it's because of our love for one another; I think it's just that we naturally have the same output as each other. People can increase their romantic/serious output, but unless they change their whole personality, I think it's more of a forced thing. Anyways, if you've been leading him in all this and he's comfortable with that and doesn't know you're not, then it's easy to just keep letting you lead. He might think you enjoy leading or something, too. Maybe make your wants known? But don't hurt his feelings.
So yeah, I believe it's not gender-based but individual-based. Guys can lead in relationships, and that sometimes feels more normal because males are supposed to be dominant or some such evolution thing. So when it's a girl leading, it might feel more abnormal. I don't know, seems like he just naturally doesn't give as much output as you. If he knows you want him to, he might try to do it more.
I'm enjoying my relationship. Our gives and takes are balanced. But I'm just lucky.