What does it mean to dream about someone constantly?

It depends on what happened in that dream with that person. Google search it. As far as I know, someone appearing in your dreams a lot has no specific meaning.

I was told once dreams are never about the person in the dream. This has held true for me as I have deep insight throughout the unconscious and can with certainty find what my dream is a symbol of through simply remembering it and then knowing through feeling why this happened. This is why it is so stupid when people ask others to interpret dreams. Your dreams are your brain. It is that simple. If you are afraid of divorce perhaps your dream will be about falling from a plane. But if you are not married then that would perhaps not be your fear and falling from the plane would mean something else. A dream is an inkblot you can use to help develop a better understanding of yourself. Otherwise it is simply a dream. This is true for art or anything in the world in general. Giving significance to things in a way that can't be tested is subjective. And is nonessential. Everything is one. Everything is meaningless. These divisions are fear and the ego. There is no self.

Maybe you should try talking to them, seeing if anything gets clearer. Maybe you're meant to be friends.