Desire is what pushes your happiness to the future. It is the block that sits between you and happiness. Bigger the desire, the further away you have pushed the happiness. As your desires reduce, your happiness increases. When desire is zero, happiness is infinite.
The joy, pleasure or bliss that one experiences when a desire is fulfilled is not because of the achievement. It is the experience of a state of no desire. In the achievement of the desire, the desire no longer exists. It was the desire that was creating the misery. In the state of no desire, the peace and happiness that is our natural state, shows up.