After some time with you the narcissist gets bored and the fuel you are providing the narcissist begins to feel old and stale. They begin to devalue you as a way to extract negative narcissistic supply. It a way of getting you to supply them in a different way. You are not doing it for them any longer. Just like a drug addict needs more of the drug for the desired effect. Your reaction, your emotions, to the devaluation is fueling them. They receive narcissistic supply from the positive or the negative. Just so your attention is focused on them. If you had an emotion or reaction to something which was not about them, this would irritate them. They get bored when things are going smooth and they like to create chaos. They run hot and cold. Everything is about fuel to the narcissist. After extracting negative supply they offer a respite period throwing you crumbs to keep you hooked into the abuse. They will keep you confused by their hot and cold behavior. There is a cycle to their abusive behavior. The cycle never ends. The relationship never gets any better. You stick around hoping things will get better and the narcissist will wake up and finally see your value in the relationship. They never do. This cycle is repeated over and over in each new relationship.