Katie, I'm really sorry you are going through this, it must be very hard. I'm also going to say I think by not considering counseling you may be giving up on your relationship too quickly. If I remember correctly you are barely 21 (if not still 20), and you say that you have already waited through 2.5 years of engagement. Well truthfully to me a 21 year old saying he's not sure he's ready to get married is not the end of the world (or always the relationship). Most people change a LOT in their early twenties-more than you even realize, saying that because your ex-FH was not ready to marry you during a time of such major change you will never get married, seems a bit over the top.
I know there are probably people here who won't agree with me on this, but are you sure you haven't become so attached to the idea of getting married young, that when your guy backed up you just gave up? If my memory is correct, you all became engaged when you were 18, I personally don't feel like dating while you still are a minor and haven't 'been out in the world' that much really counts. I think a good rule for judging your own relationship, is how well you function as a couple when you start breaking away from your parents, not how you functioned when you were basically still a child. I so know, someone is going to say something about 'being mature for your age', but I was that girl too, so I don't really buy into that line of thinking. I know that is some areas of the country getting married at a young age is common, and there is nothing wrong with it. I do think, however, that saying your guy can't say he wants to postpone, get counseling, and think about things, says to me you might be more concerned about getting married than really wanting to be sure you are ready to get married (it seemed like a bit of trying to scare him into marrying you despite his concerns-his concerns are valid and should be addressed).
In short I know you are shocked and hurt to say the least, but if you two days ago thought he was the guy for you, it wouldn't hurt to at least hear him out.