Exploring the temporal sequence between two events in psychotherapy can help to shape clinical guidelines used to indicate which interventions can positively and negatively influence a treatment’s trajectory as well as outcome. For example, a therapist’s increasing directedness in session might subsequently increase a patient’s anxiety, leading to her erotization of the therapeutic relationship. The sequential relations between two sets of process variables and an outcome variable were explored in a 5-month, three-times-per-week individual psychotherapy of a psychiatric inpatient with borderline personality disorder using simulation modeling analysis (SMA). The two sets of process variables included (a) session prototypes of three treatment models (transference-focused psychotherapy (TFP), dialectical behavior therapy (DBT), and mentalization/reflective functioning process (RF process) and (b) four previously identified interaction structures (i.e., patterns of reciprocal interaction between therapist and patient) that uniquely characterize the therapeutic relationship. The patient’s psychological distress represented the outcome variable. A decrease in psychological distress preceded an increase in the collaborative relationship. An increase in therapist directedness preceded an increase in erotization of the therapeutic relationship. Increases in the TFP and RF process prototypes preceded a decrease in the collaborative relationship. An increase in the TFP prototype also preceded decreases in the DBT and RF process prototypes. Effective treatment takes into account the uniqueness of the therapeutic dyad. Residential facilities can use SMA to assess process change in psychotherapy conducted on psychiatric units. It is important to determine whether adherence to manualized treatment models and interaction structures actually causes or merely correlates with treatment improvement. (PsycINFO Database Record (c) 2018 APA, all rights reserved)