A key question concerning social collective emergent properties is whether the asymptotic state of the dynamics reflects consensus or fragmentation and polarization of the group. In this line, we are seeking to understand the mechanisms underlying some of the public divisions (polarisation) observed in society. To do this, we present a stochastic dynamics model of coupled evolution for the binary states of nodes and links in a complex network. In the context of opinion formation node states represent two possibleopinions and link states represent positive or negative relationships.Our results give support to the claim that negative interactions are a major cause of social polarization. Moreover, we connect this mechanism to the problem of the sustainability of socio-ecological systems.