Mabe he is not ready for a deep committment. just try to respect the way he feels and dont pressure him into telling you the reasons and if he really does love you then he will come back and explain everything to you. just give it time.

Hey gurl, i hope ur ok.... it sucks i konw. To lose ur first love. Maybe it was not met to be. Dont keep ur self down about him. If it is met to be it will work out trust me i have been there done that. But i hope everything works out for the best good luck.