In this talk, I will present (1) a comprehensive library of state-of-the-art simulations of tidal disruptions of stars by massive black holes, (2) 3D simulations of common envelope ejection leading to binary neutron star formation, and (3) a self-consistent physical model of the structure of AGN disks with embedded stars. Tidal disruption events (TDEs) can be used as tools to understand massive BHs and nuclear stellar populations, the physics of super-Eddington accretion, and the dynamics in galactic centers. I will present the STARS (stellar TDEs with abundances and realistic structures) library, an interpolated grid of TDE simulations that provides the mass fallback rate to the black hole for any stellar mass, stellar age, and impact parameter. I show that all of our simulations can be reduced to a single relationship that depends only on stellar structure (characterized by a single parameter) and impact parameter. I will present simulations of TDE disk formation and the disk chemical structure—a key step in understanding the spectra of these events. I will present a systematic study of TDE host galaxies in the context of the local galaxy population. I will show that TDE host galaxies have atypical photometric properties compared to similar, “typical” galaxies, and in particular that TDE host galaxies are highly centrally concentrated. I will also present new 3D hydrodynamics simulations of common-envelope ejection and binary neutron star formation, leading to gravitational wave and electromagnetic radiation. This new theoretical framework will allow for the modeling of virtually any binary star system. Finally, I will present a self-consistent physical model of the structure of AGN accretion disks with embedded stars, accounting for momentum and energy feedback from stellar and compact objects. This modeling establishes a new regime for AGN disks outside of 1 pc and explains the metallicities of AGN.