Departing from conventional density functional theory approaches, this study employs, for the first time, molecular dynamics simulations to investigate gemcitabine adsorption on the inner and outer surfaces of BNNTs with five chiralities: (7,7), (8,8), (9,9), (8,6), and (11,0). The primary innovation of this study lies in identifying a "diameter- and chirality-dependent interaction map," which expands upon existing knowledge in three key areas: (i) an "adaptive intra-tubular contact index" showing that at smaller diameters (9.52 Å), Gem interacts via vdW forces from multiple directions inside the nanotube, but primarily through π-π stacking on the exterior; (ii) an inverse relationship between diameter and internal interaction energy (from -250 to -179 kJ/mol as diameter increases to 12.20 Å), termed "multi-directional spatial confinement"; and (iii) the first MD evidence of nanotube structural tilting at diameters below 10 Å to optimize drug binding. The quantitative findings reveal three key innovations: (1) strongest interaction for inner BN (8,6), demonstrating a 2.5-fold greater binding affinity as compared with its outer surface; (2) at 8.61 Å, exhibited the maximum hydrogen bonds (1.011) for narrowest nanotube (11,0) introducing a phenomenon termed "curvature-dependent hydrogen bond density"; and (3) enhanced BN water solubility after drug adsorption, facilitating the development of self-solubilizing nanocarriers. Based on these findings, two practical strategies for drug delivery are proposed: BN (8,6) for strong and stable adsorption, and BN (9,9) with minimal contact area (3.53 nm²) for high drug loading. This work establishes a foundation for future multi-drug simulations and physiological release tracking for smart BNNT-based nanocarriers.