This chapter uses the changes to the legislation in Canada’s Income Tax Act, implemented by the Modernization of Benefits and Obligations Act, and the subsequent cases on the meaning of ‘common-law partner’ or unmarried spouse as a method of deriving evidence about the texture of the lives lived by adults in personal relationships. From that evidence, I seek to contribute to the social history of the margins of conjugal relationships between adult members in a post-legal-equality world in Canada. The project of this chapter is not to be prescriptive about how Canada’s tax legislation should be changed. Rather, it is to use changes to Canada’s tax legislation as a prism to see something about what proximate adult relationships in Canada at the margins of conjugality look like.