(1) I don't follow.
(2) I'm not following.
I know the meaning of these 2 sentences. But I don't know what the difference is between them. Is that the second sentence puts more emphasis on the ongoing nature of the action of not understanding what the other is saying?
The context is like this:
My friend is angry about her husband, and she is saying a lot of thing to me. I can't catch up and understand what she is saying. Which sentence should I use ?