Optical frequency domain reflectometry (OFDR) with high spatial resolution was employed to locate fiber breakpoints in a resin-filled optical cable splice closure. The strain distribution along optical fibers during resin curing and temperature variation was also measured to clarify the mechanism of resin-induced fiber breakpoints. A breakpoint was identified in a blue fiber at a distance of 4.514 m from the detection port. Besides, the highest additional strain exceeding 3500 με was measured under a temperature change of 30 °C, corresponding to a thermal strain sensitivity of 98.1 με/°C for the resin-coated fiber. The breakpoint was therefore attributed to fatigue-driven defect growth caused by repeated thermally induced strain under outdoor temperature variations. Moreover, fiber layouts with different curvatures were also investigated to achieve an optimized diameters at 30 mm. These results present a micron-scale approach for detecting fiber breakpoints, elucidate the mechanism underlying resin-induced optical fiber breakage, and offer practical guidance for the arrangement of optical cables.