In this paper a cognitive model is presented for sharing behaviour (retweeting) on Twitter, addressing the underlying cognitive and affective processes. The model explains how the use of emotions in addition to information can cause an amplification in the diffusion of this information. It was designed according to a Network-Oriented Modeling approach based on temporal-causal network models. By mathematical analysis of stationary points it was verified that the implemented network model does what is expected from the design of the model. In addition, the equilibrium equations of the network model were solved algebraically by a symbolic solver and the solutions were shown to relate well to empirically expected outcomes. Validation by parameter tuning was also performed, and also shows a good approximation of empirically expected outcomes.