The notion of romantic love is something that started to take root in around the fifteenth or sixteenth centuries at least if we are looking at things from a relatively Eurocentric point of view. Shakespeare was among the first playwrights to start talking about romantic love and turning it into a highly popular idea, and there is a pretty good chance that a lot of your opinions on love come from concepts that the Bard himself managed to originate thanks to his immense talent.
The truth of the situation is that these ideas about love might make you think that breaking up with a girlfriend is never a good idea. There might also be indications you love your ex-girlfriend, something that would make life considerably more difficult for you for really obvious reasons. If you are still in love with your ex, you would first and foremost want to understand why this is happening to you, and the fact of the matter is that it has a lot to do with the human desire to feel wanted and loved in every single way imaginable.
This is because of the fact that we are simply not designed to be alone. We are social animals that require interaction with other members of our species, and not having a girlfriend can make you think like your life is not really headed in the right direction at all. Try to make sure that you are not idealizing your ex when you think about her. If your thoughts of her are objective, that might actually be true love and you should act on it before it is too late and she moves on.