My spoke broke. Does it mean that the wheel is not durable? What should I do?

It doesn’t mean that the wheel is not durable. If one spoke brakes, it means that the others around it were not tightened enough, so all the load was applied to one of them. We always add spare spokes just for this kind of event—please swap the spokes for a new one. Correct spoke tension is crucial for wheel durability. Please check spoke tension before each ride, especially at the beginning on a fresh wheel.