In the workplace, people seek positive emotional experiences as well as instrumental resources while doing their work. Yet we know little about how affective micro-dynamics drive the evolution of organizational networks, influence network trajectories, and determine macro outcomes such as collective affect and overall network structure. Given the lack of theory on affective micro-dynamics and network evolution, we propose a model that includes both affective and instrumental micro-mechanisms and use simulation methods to explore evolutionary dynamics and develop new theory. The core of our model is the empirically observed tendency for people to forego the acquisition of instrumental resources to avoid a decrease in positive emotion when choosing interaction partners. We conduct “experiments” with the simulation, considering the effects of the tradeoff, dispositional affect, resource inequality, and ingroup favoritism. The results show that dispositional affect and the tradeoff have considerable effects on network trajectories, collective affect, and resource transfer. We provide new theoretical propositions about affect in organizations.