Lol, good relationships (of the opposite sex) need trust, and trust is only earned over time. For some it takes less time, for others it takes a while. Also, sometimes they want to be friends with you. Other times you need to be the one to step out and get to know them. For example, some girls have talked to me first and we became good friends within like a few months. But, there has been another case for me where I was the one who actually first talked to them and it literally took a few years before I became good friends with her... Interestingly enough, she revealed to me recently that she generally has trust issues... So go figure.
By the way, sometimes you speak to someone and never speak to them again, even if you hoped to be their friend. It's just the way things are.
Also, there's no need to be all complicated about this. Just be nice and go with it. It's quite simple really.