Brotherly or boyfriendy?

If he's known you for quite a while, then most likely he's just being "brotherly." It sounds like he's very comfortable with you and enjoys being around you, maybe just not romantically. The best thing to do is just start being more and more flirty with him and see how he reacts... just see if he still acts like a friend or like more. When you feel confident enough about it, just let him know how you feel. If nothing else, he will appreciate you being hinest with him.