What does the simile “he gazed at me a omg time as if i were a slot machine into which he had, without results dropped a nickel”mean

It means that he is looking at her as if he is expecting something. If you drop a nickel into a slot machine and nothing happens, you're going to keep looking at it with disappointment and expectation. This feels to be the way he is looking at the narrator, as if she is disappointing him or he is waiting for her to give him results.