The scalable preparation and functionalization of two-dimensional (2D) boron nitride (BN) are crucial for its practical applications. Herein, hydroxyl-functionalized BN (OBN) nanoplatelets have been successfully synthesized through a novel two-step method, involving a simple ball milling of bulk BN powders in the assistance of sodium hydroxide, which combine the synergetic effect of mechanical shear forces and chemical peeling, followed by annealing under air condition. The obtained OBN nanoplatelets result in high solubility and form stable dispersions in water or various organic solvents that can be utilized for multiple applications. Then, OBN nanoplatelet was used as platform for embedding supermolecular aggregate (DPCS) via ionic bonding and electrostatic interaction between dicyandiamide and multivalent anions phytic acid connected with cobalt ions (denoted as DPCS@OBN). It is noted that introducing well-characterized DPCS@OBN nanohybrids significantly improve the flame retardancy of epoxy acrylate (EA), i.e., 42.7% and 48.3% reductions in peak heat release rate and total heat release, respectively. In the case of EA/DPCS@OBN system, the storage modulus at 25 °C was dramatically improved by 80.7%, and glass transition temperature was shifted to higher value; the friction coefficient value of EA/DPCS@OBN3.0 composite sharp decline to 0.077, which can be belong to the “superlubrication” phenomena. The excellent properties of these EA composites result from synergetic coupled effect between DPCS supermolecular and BN ultrathin nanoplatelets, as well as good interface interaction between DPCS@OBN and EA matrix.