Dreams are often very confusing. People see dreams that they don’t understand all the time, and as far as we know these dreams are just random images that your consciousness is paying attention to while you are asleep and they don’t really have all that much of an impact on the kind of life that you are going to end up living on a day to day basis. When it comes to dreaming about an ex-girlfriend, though, this is a sign of something greater and it is the sort of thing that you wouldn’t want to ignore because of what it usually tends to represent.
When you dream about an ex that you once had chances are that you are just missing them and that you want to reconnect with them. You would probably wake up with thoughts of them consuming you, feeling almost like an obsession of sorts. It is important to note that this is actually fairly natural and is therefore not the sort of thing that you would want to end up worrying yourself with especially if you don’t do anything rash or drastic after having seen the dream.
That said, the dream is definitely a powerful symbol that you should act on responsibly. It can potentially be a sign from the universe that you should contact this ex again. It doesn’t have to be heavy handed or romantic either. You can just get in touch with them and catch up, using your dream as a funny anecdote that would break the ice and potentially rekindle the feelings that the two of you had for each other or it would at least result in a pleasant conversation for an afternoon.