We present a large-scale, qualitative interview study that examines how an intimate technology within reproductive health comes to be chosen and trusted as a mode of contraception and how its use is shared between partners. We conducted 133 semi-structured interviews with primary users of Natural Cycles, focusing specifically on its use as a digital contraceptive. Our interpretive analysis, first, sheds light on perceptions of risks and benefits, along with how, and by whom, the decision to adopt Natural Cycles got made. Second, we discuss participants’ and their partners’ gradual development of trust in the system, and how this intertwines with interpersonal trust. Third, we consider the shared use of Natural Cycles, including partner involvement in temperature tracking, the sharing of intimate data, and navigating specific choices and risks regarding sex and contraception. We make a primarily empirical contribution to Computer Supported Cooperative Work (CSCW) research on shared uses of technology and the sharing of intimate data, and highlight avenues for future work to foster understanding of intimate technologies and their shared use in relational settings.