The breakup of liquid jets moving through a secondary fluid is a complex and important physical phenomenon, necessitating meticulous numerical simulations due to its multiphysics nature. This phenomenon is present applications such as inkjet printing, microfluidic systems, and spray atomization, where achieving precise control over the flow behavior is highly sought. The present study conducts a numerical investigation into the spatial instability of an axisymmetric capillary water jet in air, employing the diffuse interface method across a range of Reynolds numbers. To accurately resolve the interfacial dynamics and capture the physics occurring across different time scales of motion, the study employs adaptive mesh refinement (AMR) combined with a second-order accurate adaptive implicit time-stepping scheme [1]. The transition mechanism from dripping to jetting is characterized, and the temporal and spatial features of multiple jet breakups are analyzed under varying inlet velocities. The study further quantifies the impact of gravity on the non-uniform spacing of daughter droplets following breakup. Additionally, the energy transfer during the motion of the liquid thread is analyzed across multiple breakup events, considering the contributions of the kinetic energy, potential energy, and mixing energy in the two-phase flow. The numerical results reveal that the jet breakup events occur at approximately equal time intervals, while the pinch-off distance demonstrates non-linear growth in time, particularly at higher Reynolds numbers and increased jet momentum. Energy analysis highlights that each breakup event corresponds to a significant reduction in the system’s kinetic energy. The numerical findings of this study facilitate the control of flow behavior by adjusting the nozzle inlet velocity and offer new insights into the underlying physics of flow instability.