Dr. Miller was a psychiatrist that treated Alison Parker when she was having terrible nightmares about her family's basement. While he was treating her, she formed a little crush on him and began having romantic dreams about him.
When Billy Campbell started getting jealous, he confronted Dan in his office and warned him not to hurt Alison. Dan dismissed Billy and got back to work.
Dan later told Alison that he didn't have feelings for her, which made her want to leave. Dan then told her that her problem is that she won't let people love her, because she will end up hurting them.