Your dream is a common one. The old ex-lover dream. It feels so good in the dream, so right. Why did I break up with her/him? Is my dream telling me that we made a mistake and belong together?
The short answer is... no!
As disappointing as that might seem, once you understand the symbol of an ex in a dream, the sooner you can attend to finding what you want. Here's a link to the definition on this site:
ex-lover
It will explain not not why you had the dream, but help you begin to identify what aspects of that relationship you are currently missing. That missing connection in your waking life is what your ex symbolizes in your dream. There's an even better definition of an ex in a dream on the homepage of this site (in the Listen Now! section) that explains ex-lover dreams.
The good news is that once you identify those great qualities that you've been missing in a relationship, you can go out and find it. The reason why your ex isn't likely to be "the one" is that that there were other factors that made your breakup mutual, and odds are those haven't changed.
Hope that helps and makes your search for a good partner that much easier.