Digital contraceptives are intimate technologies that support their users, and their partners, in preventing pregnancy. These technologies rely on basal body temperature data to predict ovulation and calculate a fertile window, where there is a risk of pregnancy if partners have unprotected sex. Although their use is shared and relational, these technologies are mainly designed for a primary user — the person who can become pregnant. We turn our attention to secondary users of digital contraception (i.e., sexual partners), specifically, Natural Cycles. We investigate how secondary users are designed for and how primary users imagine them to be. We contribute empirical insights on how secondary users are and are not involved in digital contraception and conclude with three design proposals describing how digital contraception tools could be designed to involve secondary users. We discuss how designing for secondary users of intimate technologies requires balancing their potential as co-users and adversaries.