Who is Drewe Cole from Mortal Fear and what is their importance?

Drewe and Harper have been married three years at the beginning of this story. She is an OB/GYN and is feeling the need to have children though Harper is reluctant because of a secret he holds that he fears will end his marriage. Drewe figures out that the killer is likely a doctor who is harvesting the pineal gland from his victims with the plan to implant them into living recipients. Drewe eventually learns that Harper had an affair with her sister, Erin, and that there's a child of that union. After some time, she comes to believe she can live with the situation. Drewe asks Harper to move from their farmhouse in Rain, Mississippi, and they are packing to leave when the killer contacts Harper again. He has become obsessed with Drewe and Drewe spends some time with him online in an attempt to have him remain stationary while the FBI arrest him, but then learns that he is actually outside their home.