This randomized controlled trial will test whether promoting the novel condom CSD500 (Futura Medical Developments; Surrey, UK) for improved sexual pleasure results in couples having less unprotected vaginal sex - measured with a biological marker of recent semen exposure - compared to the promotion of a standard condom for disease and pregnancy prevention. CSD500 contains an erectogenic drug and was developed to improve sexual pleasure by increasing penile firmness, size, and erection duration.