Suicidal ideation (SI) is dynamic and closely tied to social context, yet most work treats these links as static or unidirectional. We tested a transactional account whereby SI and interpersonal appraisals co-evolve over hours and examined personality trait moderators. Young adults receiving behavioral treatment who endorsed SI and/or suicidal behavior in the past four months (N=140) completed 21 days of ecological momentary assessment (7 prompts/day). At each prompt, participants reported current SI and rated interpersonal strain (rejection/criticism/exclusion/stress) and enrichment (enjoyment/connection/meaning/support) from interpersonal interactions. Dynamic structural equation models estimated five features of SI: reactivity, generation, inertia, instability, and intensity. Negative Affectivity, Detachment, and Disinhibition trait domains were tested as moderators. Interpersonal strain was associated with higher subsequent SI (reactivity), and higher SI was associated with higher subsequent strain (generation). Likewise, interpersonal enrichment was associated with lower subsequent SI, and higher SI was associated with lower subsequent enrichment. Detachment uniquely moderated these dynamic processes: higher Detachment was associated with larger SI increases after strain and larger SI decreases after enrichment, as well as higher SI intensity and instability, higher strain, and lower enrichment. Facet models indicated that Anhedonia concentrated Detachment-related risk (higher mean SI, higher strain intensity and instability, lower enrichment, higher SI inertia and instability, and stronger reactivity to strain/enrichment). In contrast, Intimacy Avoidance was associated with lower strain instability and lower enrichment intensity. Negative Affectivity and Disinhibition did not moderate dynamic paths. SI was linked to interpersonal appraisals through short-cycle, bidirectional associations that were moderated by Detachment, especially its Anhedonia facet.