Hi Justin86.
I have your problem. If I be myself I end up the nice guy who she just wants to be friends with. If I try and be more take charge it just looks fake because it's not me. Either way it just doesn't happen.
Like you I've had girlfriends, I've even been married. But it wasn't by design, none of it.
I suppose you could study how to attract the opposite sex. I think for those of us who lack natural attraction skills we make up for it with a bit of psychology. But I'm not one for games and I don't like being played neither.
Personally, I'm at my happiest when a girl comes on to me. I think that a girl can easily figure that out about you so if they want you they will come. If you are not a natural at being more assertive like a traditional man they will suss that out and it will be a turn off for them unless they have a strong sex drive and grab you anyway.
Just don't force it and try and find the natural talent in you.