Final answer:
The narrative provides an example of cohabitation, where Jill and Jack have transitioned into living together organically, a phenomenon that is increasingly common and socially accepted.
Step-by-step explanation:
The scenario described is an example of cohabitation, where Jill and Jack have gradually started living together without a formal agreement or acknowledgment. Cohabitation often happens organically, as a couple spends more time together and begins to share living costs and spaces. As in the provided narrative, one or both partners may not immediately realize they have entered into a cohabitating relationship until significant changes in their living arrangement have occurred. This reflects social shifts noted in research data, which suggests that many couples view cohabitation as a step toward marriage, or as a 'trial run' for a more permanent partnership. Currently, living together before or instead of marriage is increasingly common and tends to be more socially acceptable.