In two-dimensional (2D) electronic devices, heterointerfaces between dissimilar 2D materials are essential for mechanical support and electrical integration, yet they can alter interfacial electronic structure and reaction kinetics. The long-term influence of interfacial material pairing on reactivity under ambient exposure remains poorly understood. Here, it is revealed that oxidation of 2H-MoTe_​2 proceeds rapidly through defect-driven pathways on insulating layers, whereas metallic contacts strongly suppress such degradation during extended ambient exposure. This suppression arises from the rapid delocalization of oxidation-induced carriers into the metallic layer, as confirmed by first-principles calculations showing long-range electronic perturbations, which lowers local reactivity and favors gradual basal-plane oxidation. To further elucidate the role of oxygen and moisture during ambient aging, controlled exposures to these species are performed, revealing that oxygen primarily drives basal-plane oxidation while moisture accelerates defect-site corrosion. The work on heterointerface-mediated charge redistribution and active species-induced degradation provides a framework for examining oxidation mechanisms in air-sensitive 2D materials and for designing passivation strategies to achieve long-term stable device integration.