Traumatic brain injury (TBI) can have serious consequences for people’s physical health and the quality of their romantic relationships. Less clear, however, are the interpersonal dynamics of couples navigating the aftermath of TBI. We used data scraping techniques to capture five years of posts submitted to online help-seeking forums, and we analyzed the resulting 349 single-spaced pages of data using codebook thematic analysis. Both TBI survivors and partners reported the focal themes of personality changes and relationship changes. TBI survivors emphasized a lack of understanding that led to grief and loss, relational uncertainty, and isolation. Partners reported poor treatment that culminated in negative emotions and relational uncertainty. The data showed notable similarities and differences between TBI survivors and partners. We interpret the results via four prominent theories of marriage and family relationships: ambiguous loss theory, relational turbulence theory, the theory of resilience and relational load, and family systems theory. Overall, our findings shed light on interpersonal dynamics after TBI and lay a foundation for future theoretical and clinical advances.