What are the motifs in Angle of Repose by Wallace Stegner?

Infidelity is a recurring idea in the novel. Three marriages are affected by it. Susan and Oliver’s marriage is ruined by Frank and Susan’s relationship. Whether or not they had a sexual relationship is unknown, but Susan has feelings for Frank and this leads to the destruction of her marriage. Oliver stays with her, but there marriage is a loveless one with no touching or words of kindness. Lyman’s wife leaves him for his surgeon when Lyman can use her support the most. Shelly Rasmussen leaves her husband because he cheated on her with multiple women.