The Rest of Our Lives by Ben Markovits

Twelve years ago, when he found out his wife Amy was having an affair, Tom vowed to leave her once their younger child went to college. That day has come, as Miri is leaving for Carnegie Mellon. After dropping Miri off in Pittsburgh, Tom heads west, visiting his brother in South Bend, an old girlfriend in Las Vegas, eventually arriving in California to see his son, Michael. However, a mysterious illness is dogging him as he reflects on the relationships and the choices he's made. A meditative novel of one man's life.