Understanding hydrogen's interactivity with storage materials is essential to a hydrogen economy. Using neutron diffraction, isotherm measurements, and inelastic and quasielastic neutron scattering from hydrogen in stage II potassium graphite intercalated graphite, we have made a comprehensive study of hydrogen self- and host-interaction at a range of temperatures (10-120 K) and pressures. We have identified rotational and translational quantum states and have modeled these using phonon-generated simulated neutron scattering and diffusive scattering from quantum-corrected or delocalized molecular dynamics. We have also modeled hydrogen's hydrodynamics and predict a large elevation of the melting temperature due to nanoconfinement.