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Hi, I'm Mike G and I'll be assisting you. Having only a black and white at the switch indicates a miswire at the fixture. Open it up and tell me the count, colors and connections.
From your description the feed is in the switch box to the one light, which means the fixture should only be connected to one set of wires and the other dets connected by themselves. The fixture is being fed from 2 sources.
Do you have a 2 wire voltage tester?
You need to identify the wires from the dimmer and connect only them to the fixture. Then connect the others together.