It is very common for people to dream about ex-partners. Individuals that have been an important part of our lives continue to take up a part of our mind and heart. It is impossible to very dramatically shut the person out of thoughts and feelings. Just because the relationship ends does not mean that all is finished. As we go through relationships we learn and at times pick up "battle wounds." You will continue to dream about your ex-girlfriend or boyfriend until you "let go" of them on a very important level, or until you learned your lessons from that relationship. Either way, dreaming about your ex-romance does not predict future involvement. It may be wish-fulfillment, reliving memories, or working out old issues. Dreams are very rarely prophetic. ;)
You did not want the relationship to end?
"..And if you can't be with the one you love, love the one your with..."
- from 'Love The One You're With', by Crosby, Stills, Nash & Young
In my; opinion, i think it means, "you don't know what u got until it's gone".