@brianbaxter1995,
He seems to be giving you really mixed signals. He has a girlfriend, but he spends the night with you and it's at least semi-romantic. There is certainly a lot of touching involved and it gives forth the impression of intimacy.
With the girlfriend being secret, it gives forth the impression that he doesn't care for her or at least that he can't bring himself to let others know about her. Which is weird (if I were her - if she exists at all, I might add, and I am skeptical about that - I wouldn't stand for that bullshit).
Either way, I think you're going to have to talk with him. A talk is a risk and risks, by definition, are not guaranteed to go right. But I think you need to either get him to stop giving you these confusing signals or have it become a relationship or not be friends anymore. This is a lousy place for you to be in, and it is really unfair to you as a person.