Hi Nicole,
Well, as a guy who has not had a relationship, I can say its probably a case of him feeling insecure. He probably is worried that you will find a girl and leave him because you prefer girls.
Maybe you can sit him down after you graduate and have this conversation face to face? I'm assuming this happened over skype or something, and its possible he just felt insecure, so talking to him face to face will probably help.
I'm here if you want to talk
Tort