"This is duty, not desire."
Sansa Stark cries to Lady Margaery about her dashed hopes of a happy marriage. Margaery counsels the girl to make the best of her situation-Tyrion is far from the worst Lannister. He has never mistreated her and their son will be Lord of Casterly Rock and the North. The thought of producing an heir scares Sansa, but Margaery asserts she might be pleasantly surprised.
In his chamber, Tyrion Lannister drinks to numb the discomfort he feels at the thought of bedding his future wife. Bronn doesn't see the problem; Tyrion can wed Sansa and keep Shae on the side. Tyrion dreads this will only lead both women to hate him. He presents Shae with expensive golden chains and she rejects the gift. She believes that Tyrion wants to marry Sansa. When he denies this, Shae again proposes they flee across the Narrow Sea. Tyrion refuses-he cannot abandon his family duties. They both realize they'll have no life together once he marries.