Measure the voltage at the two electrical terminals connected to the starter. One is a thin wire, one is a thick one. Both should measure at least 10.5 volts during attempted cranking. If both do, and it doesn’t crank the engine, then the starter is probably failing. If one or both don’t meet that voltage test, work backwards toward the battery to find out why. If you replace both the starter and the battery I expect that will solve this problem. The fuse/relay involvement is a symptom, probably not the cause. You may have a shorted coil in the starter motor solenoid for example, which could cause this symptom. That’s part of the starter motor ass’y.