Conversation so far:
When did Pamela Harriman marry Randolph Churchill?
Pamela Harriman married Randolph Churchill in 1939.
Did Pamela Harriman and Randolph Churchill have children?
Pamela Harriman and Randolph Churchill had one child: Winston Churchill.
How did Pamela Harriman and Randolph Churchill meet?
In 1939, while working at the Foreign Office in London doing French-to-English translations, Pamela Harriman met Randolph Churchill.
What did Randolph Churchill do?
Randolph Churchill joined his father's old regiment, the 4th Queen's Own Hussars, in August 1939.

Question: Why did their marriage end?
Self-contained rewrite: Why did Pamela Harriman and Randolph Churchill marriage end?