Incorporating our best understanding of binary evolution is critical for interpreting the growing sample of gravitational-wave sources. Although rapid binary population synthesis codes have been used for decades to investigate the complex formation of binary black hole mergers, they typically rely on analytical fits of single-star evolutionary tracks and parameterized models for interactive phases of binary evolution. In this talk I will show how using detailed MESA simulations and physically-motivated models can affect the orbital period evolution of binary systems, the predicted formation paths of merging binary black holes, and consequently their merger rates. I will also discuss how we can use high-mass X-ray binaries in tandem with gravitational-wave sources to deepen our understanding of binary evolution.