Young people living with HIV (YPLHIV) in Northwestern Nigeria are burdened by the psychosocial challenges of HIV management and chronic insecurity. This study examined multi-level determinants of sexual risk behavior among YPLHIV aged 15–24 years in high-security risk zones of Sokoto, Kebbi and Zamfara States and analyzed how social work case management responds to these determinants. A qualitative-dominant mixed-methods exploratory case study design was employed, combining quantitative surveys with 48 participants drawn from ART clinics and community support groups and in-depth interviews with five purposively selected YPLHIV. Data were analyzed descriptively (quantitative) and thematically using NVivo (qualitative), informed by the social-ecological model and social work case management theory. Despite high HIV knowledge—83.3% were aware of condom efficacy and 93.8% were aware of ART — consistent condom use was reported by only 2.1% of participants and partner disclosure by just 25.0%, revealing a pervasive knowledge–behavior gap driven by stigma, relational power imbalances, economic pressure, and insecurity. Case management structures demonstrated substantial strength in coordinating care and providing psychosocial support. This study proposes the Adaptive HIV Living Model (AHLM) as a framework for understanding the pathways from diagnosis to resilient living through relational, institutional, and meaning systems. Strengthening condom supply chains, expanding youth-friendly services, integrating economic empowerment, and embedding social work within national HIV frameworks are identified as priority policy actions