Who is Patrick Graham from Mortal Fear and what is their importance?

Patrick is Harper's brother-in-law and husband to Erin. He is an oncologist in Jackson, Mississippi, and is the same age as Harper. When Erin and Patrick marry, Erin tells him that she is already pregnant and that she'll marry him only if he never asks about the child's father. Patrick later begins to badger Erin for the information. After Erin's death, Drewe determines that they won't tell Patrick the truth.