Why does he behave this way towards me?

I have a guy friend that I Skype on a daily basis. Usually he is the one that invite me to Skype with him, but once we are on Skype he doesn’t talk much or at all. So sometimes it would be quiet for an hour or two until he falls asleep on me. I would talk to him, but he doesn’t seem interested but he would tell me to still be on Skype with him. I even try to have deep conversation but it don’t work. We only flirt and joke a lot and that’s it. And once I tell him about other guys or make a joke about them he would ignore me completely.