We propose and test a comprehensive theory designed to explain seemingly contradictory relations between job demands, emotional exhaustion, and work-family conflict (WFC) reported in the literature. Using job demands-resources theory, effort- recovery theory, and personal resources theory we hypothesized that job demands would spillover to emotional exhaustion as mediated by WFC (causality model), and alternatively that job demands would also spillover to WFC as mediated by emotional exhaustion (reverse causal model). Further, we also hypothesized using loss spiral theory that a more comprehensive model representing reciprocal and cross-linked effects (causal and reverse causal simultaneously) would best fit the data. The hypotheses were tested in a longitudinal study of 257 Australian (Victorian) frontline police officers at two time points approximately 12 months apart. We used structural equation modelling and found in support of the simultaneous reciprocal effects hypothesis, that the more comprehensive model fitted the data better than either the causality or the reverse causal model. Future research should more comprehensively model the important relationships between job demands, emotional exhaustion, and WFC to reflect their complex interplay. Interventions to reduce work demands arising from work pressure and emotional demands are indicated to prevent conflict at home and emotional exhaustion in police officers.