When people interact, their behaviour tends to become synchronised, a mutual coordination process that fosters short-term adaptations, like increased affiliation, and long-term adaptations, like increased bonding. This paper addresses for the first time how such short-term and long-term adaptivity induced by synchronisation can be modeled computationally by a second-order multi-adaptive neural agent model. This neural agent model addresses movement, affect and verbal modalities and both intrapersonal synchrony and interpersonal synchrony. The behaviour of the introduced neural agent model was evaluated in a simulation paradigm with different stimuli and communication enabling conditions. The outcomes illustrate how synchrony leads to stronger short-term affiliation which in turn leads to more synchrony and stronger long-term bonding, and conversely.