A many-particle consideration of diffusion-influenced reversible pseudo-first order reaction A + B reversible arrow C + B is presented. It is shown that the lowest order (in concentration) of the memory matrix is not sufficient for describing the binary kinetics of the reaction. Binary kinetic equations describing both stationary and nonstationary stages of the kinetics have been obtained using diagrammatic representation and selecting the necessary diagrams. Comparison with the fully renormalized kinetic theory is made by considering the contact approximation for reactivity.