Many people after suffering from a break up, remember their ex. And if they are single they speak to them, some people don't want anything to do with their past life. But if you were in a relationship for years and broke up, would you talk back to your ex or even want to see them again five years later when you are in a current relationship?
The past is the past and if you really love your current partner more than anything in the world, and want to spend the rest of your life with them, why bring your past life in your future? Also think about how you would feel if your partner was talking to their ex. If you are single and were waiting for the one special person for so long it's different, but if you’re in a relationship and still think about your ex, there might be a problem.