Betty discovers her husband "Don's" true identity in the previous episode, and tonight she confronts him with it!
"Don" informs her that his real name is Dick, and that he switched identification tags with fallen comrade Don Draper in the Korean war, assuming his name, cutting off contact with his family and creating a new life for himself, and then 'divorcing' "Don's" wife before marrying Betty. "Dick's" mother was a prostitute who died (while giving birth to him), as did the rest of his 'family'.