Men and women who became friends in the early American republic struggled with societal worries about the purity and chastity of their friendships. More so than other pairs of friends, heterosocial friends had to attend to how their friendships appeared to those around them. One of the most important ways of doing so was positioning a friendship in relation to spouses. In an era when marriage was the central structure for relations between men and women and fears of seduction and ruin were rampant, friends of the opposite sex needed to integrate their friendships within their marriages. This paper examines how men and women did so through the lens of their correspondence. Navigating a society without clear boundaries or rules for conducting a friendship between a man and a woman, individual pairs of friends improvised to create safe friendships in person and in letters. The careful intertwining of marriages and friendships they created demonstrates the way intimate social relationships were embedded in the social fabric of the early American republic.