Maybe your bf is just insecure and is afraid of losing you.
Keep in mind you're in for a new social life. He must be thinking about all the people you're going to meet, mixers with fraternity guys, you're going to get close with your sisters and all this must scare him if he really loves you and is not too sure about himself.
He is probably afraid of getting second place in your life or maybe lose any place he might have in your life. Which, sadly enough, may be the case after a while.
If this is the case, you should talk to him about where you two stand and either reassure him you would like him to be part of your new social life and to stand by your side or get ready for some sad and confusing times.
Hope this helps.