Bidirectional ultrafast fibre lasers present an attractive solution, enabling the generation of two mutually coherent ultrashort pulse trains in a simple and turnkey system. Still, the lack of a comprehensive numerical model describing steady-state bidirectional generation, and even less ultrafast soliton breakdowns and collisions, is obstructing the achievement of the performance compared with unidirectional lasers. In this paper, we have experimentally investigated real-time build-up dynamics of counter-propagating solitons in ultrafast ring Er-doped fibre laser via the dispersive Fourier transform methodology. We demonstrate that counter-propagating pulses experience independent build-up dynamicsfrom modulation instability, undergoing breathing dynamics and diverging multi-pulse structures formation to a stable bidirectional pulse train. Yet, interaction of pulses in the cavity presents the key underlying phenomenon driving formation evolution distinct form unidirectional pulse build-up. Our findings will provide physical foundations for bidirectional ultrafast fibre laser design to carry forward their application.