Long time coming / Sandra Brown.

Enhanced descriptions from Syndetics:

In more than fiftyNew York Timesbestselling novels, Sandra Brown has captivated her millions of readers with stories of charismatic love and tantalizing twists of fate. In this classic tale, a woman is reunited with the man she has loved for years--and must reveal the secret that will jeopardize her chance for happiness at last. He arrived out of the blue--a flesh-and-blood phantom from the past in a sports car as sleek and sexy as Law Kincaid himself. The world-famous astronaut was as devastatingly attractive as the first time Marnie Hibbs had laid eyes on him, seventeen years before. But she well knew the perils of falling for a ladies' man like Law. And this time she had someone besides herself to protect. Law is determined to discover who is sending him anonymous letters claiming he'd fathered a son he knows nothing about. Showing up at the Hibbs's return address from the letters seemed like a step in the right direction. Marnie swears she isn't the guilty party, but when Law meets her son, it's like a one-two punch to his solar plexus. The boy is nearly the spitting image of Law. Law can't remember sleeping with Marnie--then again, he can't remember much about his crazy past. But there's more to it than that: Marnie claims the boy isn't biologically hers. As the tension between them becomes unbearable and the attraction undeniable, Marnie is forced to reveal a long-held secret...one that might cause her to lose both the boy she loves more than anyone--and the man she desires more than anything. From the Hardcover edition.