Homelessness among veterans has dropped dramatically since the expansion of services for homeless veterans in 2009, and now engaging homeless veterans in existing programs will be important to continuing to make progress. While one promising approach for engaging homeless veterans in care is involving peer mentors in integrated services, posttraumatic stress disorder (PTSD) may diminish the effects of peer mentorship. This mixed methods study examined how interpersonal and emotional processes in homeless veterans with and without PTSD impacted their capacity to engage in relationships with peer mentors. Four focus groups of 5–8 homeless male veterans (N = 22) were drawn from a larger multisite randomized trial. Qualitative analysis identified five primary themes: disconnectedness; anger, hostility, or resentment; connecting with others; positive view of self; and feeling like an outsider. Thematic comparisons between participants with and without a self-reported PTSD diagnosis, and between those who did and did not benefit from the peer mentor program, were validated by using quantitative methods. Disconnectedness was associated with self-reported PTSD diagnosis and with lack of program benefit; feeling like an outsider was associated with program benefit. Results suggest that disruption to the capacity to develop and maintain social bonds in PTSD may interfere with the capacity to benefit from peer mentorship. Social rules and basic strategies for navigating interpersonal relationships may differ somewhat within the homeless community and outside of it; for veterans who feel disconnected from the domiciled community, a formerly homeless veteran peer may serve as a critical “bridge” between the two social worlds.