My ex is the mother of my child. I love her for that. How do I get her back?

Well... since I have to guess at all the details in order to give you an answer, I would say you probably can't get her back.

Why did she dump you? Or would you rather talk to a psychic?

I don't think that she will take you back if she does not like you, and you absolutely can not make someone love you. But, on the other hand, you can tell her that you want her back because (your opinion)..
Talk it out, maybe she feels the same way; you can not read her mind, you can not predicate what is going to happen if you try to make her like you, but she will probably listen if you speak honestly with her. It is not the end of the world, if she refuses, the only thing that matters is your son.