I'm sorry, but this doesn't sound at this point like it has much potential of morphing into a relationship. The fact that he calls you when he says he will, but not at all while he's away on business trips shows me that he's only putting in enough effort to keep you around, but nothing beyond that. I had a 'friend with benefits' who was a very nice guy....took me for dinner, was very pleasing in bed (and was very 'affectionate' in bed), and called when he said he would. The effort in between that was never there, though.....because he wanted nothing more than a casual friendship with sex involved. That's what your guy's behaviour says to me. If he was really interested, he wouldn't be making plans with friends the next day after you stay over....he'd want to be spending time with you. This behaviour says to me that he doesn't want you to think things are going anywhere further than sex and friendship.
If you want to be sure, the only thing to do would be to tell him that you are interested in a relationship with him and see how he reacts.
Live as if you were to die tomorrow. Learn as if you were to live forever. - Mohandas Gandhi