If you dream of your former lover, it means you have not given up on this person. You have some emotional bonds attached to them, even as your brain tells you that the relationship is over.
Sometimes, your old memories are triggered by something you saw during the day. This reminded you of your ex and a dream is created.
If you see dream imagery of happy times with your former partner, it can mean you had more good times than bad ones with that person.
If you saw more bad memories being replayed in your dream, it means the last impression of that ex was of a bad one.