There could be alot of changes as to why he suddenly doesn't see the relationship progressing past where it is. Him going to college is a big one. However, that is an obstacle that can be overcome as long as both of you are determined to be together and are willing to sacrifice things for each other.
Just because he is being pessimistic about the status of the relationship does not mean he does not care. It most likely means he is re-evaluating things in (most likely) a more realistic light.
Really the most you can do is ask him what is going on with this. Ask if he even wants to continue the relationship. (sorry honey, but hiding from the question and running away from it won't keep your relationship together.) Basically ask him whether or not he is commited enough to you to see this relationship through college, amoung other things.
You should also ask yourself those questions. (seriously.)