In early 2020, the novel coronavirus 2019 (COVID-19) spread across the United States and mitigation measures drastically affected the daily lives of Americans. In this study, we assessed the association between COVID-related relationship conflict and changes in intimate and sexual behaviors and experiences. Using data from an online nationally representative probability survey of 1,010 American adults in April 2020, we estimated the impact of coronavirus-related relationship conflict on changes in intimate and sexual behaviors among those in any type of romantic or sexual relationship (N_weighted=742). Further, we assessed the association between conflict and experience of orgasm and feeling emotionally close to partner. Among individuals in relationships, 34% reported some degree of conflict with their romantic partners due to the spread of COVID-19 and its related restrictions. Those experiencing frequent coronavirus-related conflict with their partner were significantly more likely to report decreased frequency of several solo and partnered intimate and sexual behaviors compared to those not experiencing any such conflict, exhibiting a dose-response trend among partnered sexual behaviors. Since the spread of coronavirus and associated social distancing measures in the United States, Americans have experienced escalations in conflict in their romantic partnerships, which was associated with changes to their intimate and sexual lives.