What does it mean when you keep dreaming about your ex is he doing the same?

No, another person's thoughts, dreams or behavior cannot influence your dreams. If such things were possible, people would not need cell phones or the internet to communicate. Dreams are produced by the dreamer's own subconscious mind and exist only within the dreamer's own brain. Dreams do not provide any supernatural insight into anyone else's thoughts or feelings.

I would say its because he's still thinking of you because when me annd my ex broke up I constantly had dreams about him and everytime I would have a dream about him he would call me and call me finally I stopped having dreams of him and completly moved fwd and he stopped calling me