Stiles has forgotten all about what Derek meant to him. When he lost his mother he did remember all the time he remembered. But then when John became an abusive drunk he lost all memory of caring for the Hales. For loving Derek.
Derek on the other hand never forgot. Niether did the Hales. They would call John but he would hang up on them. Derek even got that symbol tattooed on his back. Then he lost his family and felt like he could never love again.
Well they ever find one another again?