Negative emotional arousal during conflict has been related to negative outcomes in romantic relationships and degraded quality of family life. Despite its extensive study in psychology, it is still challenging to quantify emotional arousal in a meaningful way with objective indices beyond traditionally-used self-reported scores. We examine the association of acoustic and physiological arousal between dating couples through speech prosodic patterns and Electrodermal Activity (EDA) features. We use a dynamical systems model (DSM) approach to capture the interplay of arousal indices within and between people. The DSM parameters reflect the amount of self-regulation with respect to the acoustic and physiological cues within a person, the degree of cross-regulation between the two modalities, as well as the within-couple co-regulation. Our results through statistical analysis and classification experiments indicate a significant association between the estimated system parameters and the participants' self-reported relationship satisfaction measures. This is consistent with previous findings and can help towards better understanding regulation mechanisms and escalation effects of emotional arousal during couples' discussions.