Since "Nolan" and "Harper" are common character names in romance and fanfiction (particularly in the series by Krista and Becca Ritchie, where the couple Nolan Hale and Harper Howell is a primary pairing), here is the answer:
Based on the phrasing of your question — "who was Nolan's 'to' before Harper" — you are most likely referring to the , specifically the partners or love interests of a character named Nolan . who was nolan's to before harper