Many gay Australian serodiscordant couples are currently relying on an HIV-positive partner's undetectable viral load (UVL) to practice condomless sex. For these couples, preventing HIV is often considered a mutual responsibility, yet they lack a formally endorsed strategy that helps them navigate 'UVL for prevention' (UfP) as a couple. Drawing on interviews with 21 Australian gay men representing 15 serodiscordant couples, we explored 'the couple' within serodiscordant HIV prevention. In learning to rely on UfP, couples were initially apprehensive as they navigated unfamiliar territory, but their concerns faded over time. Confidence in UfP was facilitated by repeated condomless sex without transmission, consistent test results, and being in a couple framed by trust, commitment, and familiarity. Gay male serodiscordant couples should be encouraged to negotiate clear, spoken 'viral load agreements' (VLAs) if they choose to rely on UfP.