The therapeutic alliance, long regarded as a cornerstone of effective behavioral health treatment, remains difficult to measure and operationalize across diverse levels of care. This study examines how provider attachment style and related interpersonal characteristics—assessed through the Care Predictor Index (CPI), a 234-item psychometric instrument—predict patient retention outcomes across five behavioral health organizations. Drawing upon attachment theory, alliance research, and data from over six months of clinical practice, the study evaluates how therapist CPI scores correlate with treatment completion and discharges against medical advice (AMA) within detoxification, residential, partial hospitalization, intensive outpatient, and outpatient settings. The CPI integrates elements from the Adult Attachment Questionnaire (AAQ), the Counselor Activity Self-Efficacy Scales (CASES), and the Analog to Multi-Broadband Inventories (AMBI) to generate multidimensional provider profiles that capture attachment, confidence, and personality traits empirically linked to alliance formation. Findings demonstrate that therapists with CPI scores above 70 achieved higher treatment completion and lower AMA rates, underscoring the predictive validity of attachment-informed provider assessment. Beyond identifying measurable therapist level predictors, this analysis situates relational competence as a central determinant of program retention and proposes the CPI as a scalable mechanism for workforce development, quality improvement, and outcome optimization across the continuum of behavioral health care.